I've only had this happen via an Umber Hulk's confusion, but there's a little more to the story than that.
I'm currently playing an Elan Psion who is rather obsessed with becoming a legend. Part of this, of course, involves her being an immortal aberration. She has to hide her immortal nature from the rest of the party, especially the ranger, because he doesn't look too kindly upon the concept of undying freaks.
A few sessions ago the Binder in the party made a pact with the first elan who then became a vestige but failed the roll to control the vestige. I made a Knowlege Psionics check and couldn't help but notice who it was the Binder had merged with.
Seeing this, she comes up to me and starts asking lot of questions about elans and immortality, trying to figure out what I know because of my experience with psionics. My psion is made very uncomfortable by this whole conversation and tries to aovid the binder from that point forward. This was the first unhappy happening for these two characters. The second came some time later.
...
Flash forward, and we are battling monsters in an abandoned dwarf stronghold. Out pops an Umber Hulk, who promptly confuses the Binder. We try our best to get the Binder away from the Umber Hulk, and after we're successful, the Binder - still confused - attacks my psionic crystal. Seething with anger, I begin to wallop the Binder with my quarterstaff to little effect. After dispatching the Umber Hulk the rest of the party wades in and manages to subdue the Binder until her confusion wears off.
Everyone told me not to blame the Binder because she was obviously under some sort of mental distress, but I refuse to acknowledge this. Being a psion and an elan, I understand perfect control of mind and body, and I believe there is no excuse for losing that control (read: failing saving throws).
So now my character has two reasons to dislike one of the other PCs, and it's led to some pretty interesting roleplaying situations. So far, the animosity does not extend beyond the characters in game.