I don't know if this has been report but...
As you can see in this picture, there is still some vertical space above my main MSN Messenger window while Plus! docks the window. When I right-click on the space it shows Destop's popup menu.
Environment:
Windows Svr 2003 Trad. Chi., with UXTheme.dll patched by UXTheme multi-patcher 1.5. Using AMPed visual style with Normal font size
Plus! 2.54.74
MSN Messenger 6.1.0207 - It's the Windows X multi-skin version, but I don't know exactly what skin I am using. It has a maple-leaf looking.