[Users] What's processing marks ?

[Michael]

Hello,

What's happening here ? In an IMAP account, i was reading one mail of a thread of 2, then decided to move the two mails to another folder. Selected both, dragged with mouse, but unexpectedly a popup asked "There are some marks left to process. Process now ? (yes) (no) (cancel)" and since i've no idea what the whole thing means, and thought this would be like "do nothing", i clicked "no". (I know i should've chosen 'Cancel' instead).

Then, the thread was gone. It wasn't in the new folder, nor in the original folder, nor in the trash. It just disappeared.

Just, i never heard of processing marks, what does it mean ?