[xmonad] Mod-P blanks screen (XMonad.Config.Gnome)

Hi I'm using XMonad.Config.Gnome (at least, its keybindings) under Ubuntu 10.10 (Maverick), through gnome (with XMonad set as my window manager). My xmonad.hs is copied from another machine, which is running Ubuntu 10.04 (Lucid), where it works fine. Instead of opening the "run application" dialog, pressing mod-p (mod = left super) blanks the screen for about a second. When it comes back on, there is still no dialog. Has anybody else encountered this, or know a solution? --Max