I've been running into an interesting problem lately. I use a very basic
xmonad/xmobar setup (system info below); not much more than the sample plus some hotkeys.
Recently, when I start xmonad (either with startx or MOD+q) xmobar is
covered by any windows, as if I did not have manageDocks in my
manageHook function. However, it only does this on the screen/desktop
that is active when xmonad is (re)started.