OK. My mail is definitely acting wonky.
Uhhh... Like WOW!
My Mail.app seems to have become unreliable also. Just last night I moved a message from my inbox to a folder. It did not appear in the folder, and most definitely left the inbox. Search could no longer find it. Fortunately it was easily resent. Never did find the original. I've experienced other weirdness also, I was trying to move an item and the highlight on the folder was not appearing. Relaunch of Mail seems to restore normal behavior. I relaunch mail a lot lately it seems...