We noticed that on W7 with DPI set to > 125% or to > 100% with ("Use windows xp style dpi scaling") turned off, our fullscreen mode (which sets the client rect of our window = desktop rect of the main monitor) no longer hides the task bar like it does for other settings.
(The setting can be found in the Control Panel\Appearance and Personalization\Display section after clicking on the "Set custom text size (DPI)" link)
I found the following interesting article:
So I set out to try to work around the bug in other means than manually hiding/restoring the taskbar visibility but so far I've failed and currently believe it's a bug in W7 (and possibly vista).
The following applications also fail to work properly in fullscreen mode (the taskbar is still visible):
* Microsoft Visual Studio 2008
* Microsoft Word 2007
* Adobe Reader 9.1.3
These apps work (probably by hiding the task bar through the WIN32 API):
* Powerpoint Slide Show
I also tried creating a brand new MFC-based app and use its "SetFullScreenMode()" functionality but it fails in the same way as all other apps on the list.