[sylpheed:30015] [Bug] Cannot Exit/Quit Sylpheed when "Display tray icon" is enabled

[Michael Schwendt]

Configuration > Common Preferences > Display
[X] Display tray icon

When this is enabled and I'm in GNOME and restart Sylpheed 2.2.7, I
often (= sometimes it is not reproducible) find myself unable to
terminate Sylpheed with either

 - the Exit menu function
 - CTRL+Q
 - ALT+F4
 - the main window close button
 - Exit option in the tray icon context menu

None of those functions work, and I need to kill sylpheed. If I
disable the tray icon, no such problems. Looks like a race condition
somewhere.