Ok. So This is how Krishna described his encounter with Sage Durvasa in Anusansana Parva. The conversation is between Krishna and his Son from Rukmini.
Formerly, in my house, O son, dwelt the Brahmana Durvasa whose complexion was green and tawny.
Clad in rags, he had a stick made of the Vilwa tree His beard was long and he was exceedingly emaciated. He was taller in stature than the tallest man on earth. Wandering over all the worlds, viz, that which belongs to human beings and those that are for the deities and other superior beings, even this was the verse which he sang constantly among assemblies and in public squares.Who is there that would cause the Brahmana Durvasa to dwell in his house, doing the duties of hospitality towards him? He becomes enraged with every one if he finds even the slightest transgression? Hearing this regarding my disposition, who is there that will give me refuge? Indeed, he that would give me shelter as a guest should not do anything to anger me' When I saw that no one ventured to give him shelter in his house. I invited him and caused him to take up his residence in my abode.
On certain days he would eat the food sufficient for the needs of thousands of persons. On certain other days he would eat very little. On some days he would go out of my house and would not return. He would sometimes laugh without any ostensible reason and sometimes cry as causelessly.At that time there was nobody on earth that was equal to him in years. One day, entering the quarters assigned to him he burnt all the beds and coverlets and all the well-adorned damsels that were there for serving him. Doing this, he went out. Of highly praiseworthy vows, he met me shortly after this and addressing me, said, O Krishna, I wish to eat frumenty without delay' Having understood his mind previously, I had set my servants to prepare every kind of food and drink.Indeed, many excellent viands had been kept ready.
As soon as I was asked, I caused hot frumenty to be brought and offered to the ascetic. Having eaten some, he quickly said unto me, smeDo thou, O Krishna, take some of this frumenty and smear all thy limbs with it' Without any scruple I did as directed. Indeed, with the remnant of that frumenty I smeared my body and head. The ascetic at that time saw thy mother of sweet face standing near.Laughing the while, heared her body also with that frumenty. The ascetic then caused thy mother, whose body was smeared over with frumenty, to be yoked unto a car without any delay.Ascending that car he set out of my house. Endued with great intelligence, that Brahmana blazed with effulgence like fire, and struck, in my presence, my Rukmini endued with youth, as if she were an animal destined to drag the cars of human beings. Beholding this, I did not feel the slightest grief born of malice or the desire to injure the Rishi.
Indeed, having yoked Rukmini to the car, he went out, desirous of proceeding along the high road of the city. Seeing that extraordinary sight, some Dasarhas, filled with wrath, addressed one another and began to converse in this way, Who else is there on earth that would draw breath after having yoked Rukmini to a car! Verily, let the world be filled with Brahmanas only! Let no other orders take birth here. The poison of a virulent snake is exceedingly keen. Keener than poison is a Brahmana.There is no physician for a person that has been bitten or burnt by the virulent snake of aBrahmana, As the irresistible Durvasa proceeded on the car, Rukmini tottered on the road and frequently fell down. At this the regenerate Rishi became angry and began to urge Rukmini on by striking her with the whip. At last, filled with a towering passion, the Brahmana leapt down from the car, and fled towards the south, running on foot, over a pathless ground. Beholding that foremost ofBrahmanas flying along the pathless ground, we followed him, although we were smeared with frumenty, exclaiming behind him, Be gratified with us, O holy one!
Endued with great energy, the Brahmana, seeing me, said, O mighty-armed Krishna, thou hast subdued wrath by the strength of thy nature? O thou of excellent vows, I have not found the slightest fault in thee! O Govinda, I have been highly gratified with thee. Do thou solicit the fruition of such wishes as thou pleasest! Behold duly, O son, what the puissance is of myself when I become gratified with any one.
Why would Kuntis foster Father leave her alone with the Sage? She was at the least, 13 years in age and at the most, 15-16.
And Pritha in the house of her adoptive father was engaged in looking after the duties of hospitality to Brahmanas and other guests. Once she gratified by her attentions the terrible Brahmana of rigid vows, who was known by the name of Durvasa and was well-acquainted with the hidden truths of morality. Gratified with her respectful attentions, the sage, anticipating by his spiritual power the future (season of) distress (consequent upon the curse to be pronounced upon Pandu for his unrighteous act of slaying a deer while serving its mate) imparted to her a formula of invocation for summoning any of the celestials she liked to give her children. And the Rishi said, Those celestials that thou shall summon by this Mantra shall certainly approach thee and give thee children'
this is what she told Pandu:-
'In my girlhood, O lord, I was in my father's house engaged in attending upon all guests. I used to wait respectfully upon Brahmanas of rigid vows and great ascetic merit. One day I gratified with my attentions that Brahmana whom people call Durvasa, of mind under full control and possessing knowledge of all the mysteries of religion. Pleased with my services, that Brahmana gave me a boon in the form of a mantra (formula of invocation) for calling into my presence any one of the celestials I liked. And the Rishi, addressing me, said, 'Anyone among the celestials whom thou callest by this shall, O girl, approach thee and be obedient to thy will, whether he liketh it or not. And, O princess, thou shall also have offspring through his grace.'(she made this up since Durvasa did not say any of this to her as seen above in the speech between Kunti and Durvasa)
Kunti's conversation with Suryadev went like this :-
O slayer of foes, a certain Brahamana gave me this formula of invocation as a boon, and, O lord, I have summoned thee only to test its efficacy. For this offence I bow to thee. A woman, whatever be her offence, always deserveth pardon'
Surya Sun replied," I know that Durvasa hath granted this boon. But cast off thy fears, timid maiden, and grant me thy embraces.
Amiable one, my approach cannot be futile; it must bear fruit."
Thou hast summoned me, and if it be for nothing, it shall certainly be regarded as thy transgression' Vaisampayana continued,
Vivaswatt thus spoke unto her many things with a view to allay her fears, but, O Bharata, the amiable maiden, from modesty and fear of her relatives, consented not to grant his request.
And, O bull of Bharata'srace, Arka addressed her again and said, O princess, for my sake, it shall not be sinful for thee to grant my wish' Thus speaking unto the daughter of Kuntibhoja, the illustrious Tapana, the illuminator of the universe, gratified his wish. And of this connection there was immediately born a son known all over the world as Karna accountred with natural armour and with face brightened by ear-rings.
And after the birth of this child, the illustrious Tapanagranted unto Pritha her maidenhood and ascended to heaven.
It has been pointed a lot of times that there are many versions, translations of the epic and many are quite blunt in pointing out what just happened here. Kunti brought it upon herself with her childishness and rashness, but after a conception like this, women in today's age would opt for the other alternative options that were not available to her.So how come Sage Durvasa is not at fault? He should have informed her foster parents of the Mantra he was giving their daughter.The mantras were so powerful and needed more terse instructions that 'summon the celestials with mantra and they will give you children'. And the Pandavas were born to Pandu and kunti/Pandu and Madri with Pandus consent/orders.They both are now Pandus wives, and in that types of Son, one is the son beget upon ones wife by another man.But kunti was not married, neither did she took permission from her Father, so here Suryadeva is the sole father. He had more say in his sons life than the other gods had in their respective son's.If letting Karna be brought up in a Suta family instead of a Kshatriya family means that Kunti failed in her duty as a mother than the same goes for the Father.He knew that Kunti did not want the child, so he could have shipped him off to a childless Kshatriya family if being raised in the order of Suta was such a dire problem.