I've run into the following glitch with Mail. Messages that are listed in the main viewer window can be selected then moved to another mailbox with the Mailbox/Transfer/<mailboxname> menu option.
But, if the message is opened in its own window (by double clicking) the mailboxes are grayed out and the message can't be transfered via the menu option. This doesn't happen all of the time and appears to be completely random. It is independant of the message that is open, the mailbox it is in, and every over variable I could think to test.
Relaunching didn't fix it.
Does anyone have any ideas?