sorry, no idea. Seems nokia hardcoded something somewhere without any official documentation (heck a quick look at the documentation for .desktop files in the maemo wiki draws a blank on how Mandatory is supposed to behave).

i did manage something funny tho, when i replaced the Path line in applications-menu.desktop with the one in application-launcher.desktop. suddenly the ghost button i was troubled with earlier vanished completely, and the task switcher area started going further up then before.

so while i cant confirm it (tho i am going to check with the new version so stand by), one trick may be to replace the .desktop file with one that have a different path entry, rather then trying to set up ones own. But thats just me speculating that the reason the button vanished was because the .so seg faulted on load.