As reported over on the iDownload blog (and as mentioned to me by others), Gmail had a significant oops lately. Apparently, there was some system glitch that resulted in some actions (such as "delete" and "report spam" being applied to a message other than the one a user selected. Perhaps not all Gmail users were affected; I didn't receive the notification that other Gmail users have reported receiving.
In case you're curious, here's what the notification said:
You may have been impacted by a recent issue in Gmail that inadvertently caused some actions (e.g. delete, report spam) taken while viewing a message to be applied to a different message. The issue occurred between January 15 and January 22 and is now fixed.
We encourage you to check your Trash and Spam folders before February 14, 2014 for any items you did not intend to delete or mark as spam and move them back to your inbox. We apologize for any inconvenience.