I haven't noticed any odd camera issues other than it being able to see under the world easier if you are in 3rd person compared to previous clients, but that is exactly how it is on Live still currently.
As for the clicky problem, it makes more sense now I think. Sounds like we may have a problem with interrupting casts. If it doesn't get the interrupt and never gets the finish casting packet(s), it can definitely bug your client like that. So, maybe we just have the interrupt opcode incorrect or something. I will check it out. Thanks
EDIT: Yeah, I can duplicate the bug if I don't have a target like you mentioned. I am thinking maybe the client knows to expect the item to cast the spell, but not getting what it expects when it fails. Still investigating.