Odd behaviour while windowshaded in XFCE4

I have been having an issue with XMMS and I'm not sure if the problem is
XFCE's handling of the windows or XMMS:

I keep my XMMS windowshaded at the top of my screen and I have a 14
pixel workspace margin (in other words, the height of XMMS while
windowshaded) so that windows will never maximise over XMMS.
(See a screenshot to know what I mean:
http://uug.eastern.edu/~andrewski/misc/snapshot5.png.)  However, if I
un-windowshade either the main window or the playlist window,
the other will snap down to its bottom border, instead of keeping its
place at the top border of my screen.  Then, when I try to move it back
up, it doesn't respond completely to my attempts to move it; rather, it
will stop dragging most of the way.  I have to then regrab it and do so
a handful of times before it is back in the corner where it belongs.

I thought that perhaps the "Snap windows at XX pixels" feature was at
fault, so I turned it off, but I've still been having the problem.

Anyone know what it could be?

Thanks in advance,
Andrew