I have several email accounts that I have associated to a unified inbox via IMAP. For some time, I have sensed emails go missing. This morning it happened in front of my eyes, so I was able to investigate. I had an email come in. It showed up in the unified inbox. I opened it and replied. I was reading the next email and noticed the one I had just replied to sudden disappeared out of the unified inbox.

I searched for the subject, it was still "somewhere" and reported to be in "Inbox" Turns out it was in the "subfolder" under unified inbox relating to the account it came in to. Shouldn't all emails in the inboxes for my various accounts be reflected in the top-level, unified inbox? It is very confusing.