I'm using the Mate Desktop spin of Fedora 24 and when I try to alt-tab between claws-mail and other applications it does not behave as expected. Specifically, I can tab away from claws-mail with no problem, but pressing alt-tab again does not bring claws-mail back to the foreground. It looks like every time alt-tab is pressed claws-mail is the first item on the window list, but that means tabbing to it requires cycling through all the windows or shift-alt-tabbing a couple of times. This is fairly annoying just because it breaks a very simple and standard behavior.
Not a Claws Mail bug, it works correctly in any other environment I have ever tried it in. Looks a lot like https://bugs.launchpad.net/ubuntu-mate/+bug/1493408
Thanks for the pointer. This might even just be user-error since I can't seem to replicate it this morning anyway. Sorry for the noise.