I recently noticed that Mail on my Mac would automatically remove flags from my messages.
I had set up a rule to flag every incoming message so that I do not forget to reply to a message even if it is marked as read.
However, recently Mail started removing the flag from a message if I view it for a few seconds. I also once saw that all flags were gone without me having viewed the messages at all.
Is this a known problem? Any ideas how to prevent Mail from unflagging messages automatically?