When you maximize a window horizontally or vertically and then close to tray and reopen, the window is full-screened.
I reproduced this behavior on two machines, both running Gentoo with Xfce 4.4.2. One of these was using Xinerama, the other was not. The applications I tested this with were Pidgin, XChat, and Deluge.
***This behavior did NOT occur with Amarok.***
Steps to reproduce:
1. Open, for example, Pidgin. It needs to be configured such that when it is closed, it minimizes to tray icon.
2. Resize the Pidgin window to make it fairly small.
3. Use the keyboard shortcut to maximize the Pidgin window vertically (I believe the default is Alt-F6).
4. Close Pidgin (to the system tray in the Xfce panel).
5. Click on the Pidgin icon in the system tray to restore Pidgin.
Pidgin should now be full-screened.
There seems to be a problem in saving state when minimizing to a tray icon, and it may only occur with GTK applications.
Not an systemtray problem. The systemtray only embeds external windows. If it is a Xfce problem, it's probably Xfwm4's. Olivier any thoughts?
Well, it's the 3rd one of the same type with Pidgin. Thing is, 1) I cannot reproduce this neither on Fedora 9 nor on Ubuntu, and 2) there is no such thing as "minimize to systray", it is a misnommer as it's the app (Pidgin) that hides the window, the window manager has little to do with that process.
I think it's a bug in pidgin, but please feel free to prove me wrong.
11 years later (using XFCE 4.12), I'm happy to report that the bug no longer reproduces.