Version: (using KDE 4.2.1)
Compiler: gcc-Version 4.3.3
Installed from: Gentoo Packages
When the dashboard is displayed and you trigger the expose function either trought a press of strg+F12 or by moving the mouse in the top left corner, all windows as well as the dashboard overlay are displayed.
Imho the Dashboard mode should end when triggering expose.
*** This bug has been marked as a duplicate of bug 159519 ***