I have encountered similar problems. Once, I believe the version was 1.07, I decided to do the quest asap after I got it. So I did it as fast as possible, trashing the group, getting the egg and returning it within same turn (with only a handful of units going back to quest giver, just to be sure), and I got the dragon. Don't know what of those did the trick, but it worked.
I have missed it numerous times though. And the creature is overpowered in the wrong hands anyway. 