This seems to be caused by preventing the titlebar of a window being in the same space as the taskbar (or the area the taskbar would be, if it was positioned on the top of the screen)
Commenting the 'if' block on line 432 of placement.c in xfwm4-4.2.3.2 will enable the titlebar to be in this space, but could cause problems if 'snap window to border' is turned on, as the window will then snap to the taskbar, and if you keep moving the window upwards, it will then snap it to the top of the screen.

Comment 2 Olivier Fourdan 2007-01-21 12:51:54 CET

Seems to work fine in 4.4.

Just checked out and compiled the svn version. It's definitely reproducable.

Hold alt (or whatever key is configured to move windows) and left click on a window. Now drag this window up towards the top of the screen. At the top of the screen (or on the bottom of the panel, if the panel is positioned at the top) the window will display edge resistance.

It only occurs with the top of the screen, the sides and bottom are fine.

Comment 4 Olivier Fourdan 2007-02-12 19:11:00 CET

The window manager will prevent you from moving the window toward the top, this is an expected feature, dunno if that's what you see. If so, it's not a bug.

Comment 5 Steve Dodier-Lazaro 2015-02-07 19:48:09 CET

As of 4.11, you can push parts of a window below the screen bottom border and above the top border, but you can never get a window entirely out of the screen.

I don't think anything works unexpectedly. Should this report be closed?

Comment 6 Olivier Fourdan 2015-02-07 21:20:57 CET

Yes, should be closed.

Comment 7 Steve Dodier-Lazaro 2015-02-07 23:30:09 CET

Marked as WORKSFORME.