Ok, I've been having this issue for a while, but I just now got around to reporting it. Any idea how to fix it?
Below is a screenshot of my issue, (the shadow thingy that my cursor is pointing to) and the info from the WB page that is apparently useful..

WindowBlinds version : WindowBlinds 6.1 (build 51 x86)
WindowBlinds is installed correctly on this PC
WindowBlinds appears to be activated on this PC
Your machine supports per pixel borders on WindowBlinds skins.
(Plug and Play Monitor) 1 is attached to NVIDIA GeForce 6800 GT
(Plug and Play Monitor) 2 is attached to NVIDIA GeForce 6800 GT
Wblind.dll 2008/03/17 12:45:20
Wbsrv.dll 2008/03/11 06:56:10
Wbconfig.exe 2008/02/20 14:52:33
Wbload.exe 2008/02/14 12:05:14
Wbhelp.dll 2007/07/24 10:21:07
Wbui.dll 2007/11/06 11:13:05
Tray.dll 2007/09/12 17:58:21
Screen.exe 2008/01/14 18:02:18