In a configuration with two IMAP accounts (which is probably irrelevant):
When I removed an IMAP account folder from the folder list, it deranged the whole folder list, vanishing all account folders (IMAP and local) except for an unnamed item (turning out to be the other IMAP account) and a "Notes" item. After a few clicks, the "Notes" item disappeared as well, leaving just the unnamed item in the folder list (see screenshot 1).
Can be reproduced again and again with varying results (see screenshot 2).

Luckily, either of a restart or a switch between long and short folder list will recreate the folder list correctly. But in the meantime, I died a thousand deaths, fearing it might have deleted or corrupted my local (or even the other IMAP) folder.

Reproducible: Always