Fedora 18, XFCE 4.10, ThinLinc 4.0.0post-3958.
When you select Work area as the client window size, the resulting ThinLinc session will become larger than the maximized window (the actual work area).
Panel settings were 'default', i.e. a top panel with menus and a bottom launcher panel.
After starting a ThinLinc session with size Work area on XFCE:
$ grep Desktop ~/.thinlinc/tlclient.log
2013-05-22T14:07:01: VNC command: /opt/thinlinc/lib/tlclient/vncviewer -RemoteResize=0 -FullScreenAllMonitors=0 -FullscreenSystemKeys=1 -FullColour=1 -LowColourLevel=2 -AutoSelect=1 -CustomCompressLevel=0 -CompressLevel=2 -QualityLevel=8 -MenuKey=F8 -PasswordFile=/tmp/vncviewerZMM7YU -Shared=1 -DesktopSize=1920x1178 -Maximize -geometry=1918x1174+1+22 127.0.0.1::54473
$ xprop -root | grep ^_NET_WORKAREA
_NET_WORKAREA(CARDINAL) = 0, 31, 1920, 1120, 0, 31, 1920, 1120, 0, 31, 1920, 1120, 0, 31, 1920, 1120
Session is created larger than the maximized client window on gnome-shell as well (F18).
This problem occurs with both 4.0.0 and 4.0.0post-3937.
Given comment 2, it seems like we are not respecting _NET_WORKAREA properly. Should hopefully be an easy fix.
It was the good ol' 32-bit is long in X11 bug again that caused FLTK to fail to read _NET_WORKAREA. Fixed in r28300.
Tested using client build 4298 on XFCE and gnome-shell. Works as expected.