Simple little bug to reproduce:
it happens under windows vista ultimate.
In the Windows Display Settings, Position de Monitor #2 at the left of the Monitor #1 (Main monitor). (By dragging the monitor picture #2) (If the Monitor #2 is at the right of the main monitor, everything work well) (attached picture)
Tick the option "Extend the desktop onto this monitor" for the Monitor #2
Start a mpg or avi in BSPlayer
Now, drag the BSPlayer movie window to the Monitor #2, make it fullscreen.
Now, Right Click on the movie window on the Monitor #2. The pop Menu appear on the Monitor #1 :o
BSPlayer rocks !