I was very surprised to find out that Imoen, my bestest of buddies, is no longer cool with being in a low-reputation group. That's all fine and good, she said her dialogue and left the group. Interestingly, she did NOT leave the area as other characters would (and did, in the case of Khalid.) I was able to kill her and take her stuff back, since she just stood there. I tried speaking with her again beforehand, of course, but she just repeated her line.
Current Behavior: Imoen leaves the party at appropriate low reputation but does not walk away. She remains in the area.
Expected Behavior: Imoen leaves the party at appropriate low reputation and acts as any other good NPC would. She walks away, never to be seen again.