Hello, thanks for tips. I have got further.
I found out that the behavior is caused by claws-mail-multi-notifier and it *does* happen with the experimental versions of both packages as well (3.9.0-2/3.9.0-1). After some experimenting, I am able to reproduce it with fresh user (no dotfiles' copying). Following is complete method to reproduce. STR: 1 - Install claws-mail and claws-mail-multi-notifier 2 - Run Claws Mail (configure fake account, no need to be functional) 3 - Open Configuration -> Plugins 4 - Select Load and navigate to plug-in file /usr/lib/claws-mail/plugins/notification_plugin.so 5 - Close Plugins window 6 - Open Configuration -> Preferences -> Plugins -> -> Notification -> SysTrayIcon 7 - Enable check-boxes: "Enable TrayIcon" and "Hide when iconified" 8 - Confirm Preferences 9 - Make sure that main Claws Mail window is maximized 10 - Switch to other desktop (Ctrl-Alt-Right or Ctrl-Alt-Left) and back 11 - Observe Claws Mail window and "Window Buttons" Xfce panel > result: Window is visible (and usable), but has disappeared from the panel (and "Alt-Tab" window switcher) > oracle: Either both should be visible, or both hidden (if that is purpose of mentioned option) -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org