Smartphone application automatically poping to foreground

I created a simple test application. A main Form with
Border style "none" and no ContexMenu.
In this form I override OnPain and OnPaintBackground.
Inside OnPaintBackground I draw a bitmap to the screen.

I run this in the Smartphone 2003 emulator. The
application runs, the bitmap displays and the I press the
home key, the application goes to the background. As
expected. Then I wait with out touching anything just let
it sit, after 1 minute the application comes utomatically
back to the front. Why?

Thanks