If you have a problem with drop down menus for certain programs ( in my case kdenlive and virtualbox ) not displaying their drop down menus in xmonad it might be this issue:

https://github.com/xmonad/xmonad-contrib/issues/73

The workaround proposed by geekosaur in that bug report appears to work for me, after about ten minutes of testing.

However if you've followed the usual introductions to xmonad you'll need to change "workspacen" for "myWorkspaces", as looking at this online paste that appears to be what geekosaur calls their workspaces variable. ( It might be a "variable", I don't know Haskell ).

So copy and paste this text into the appropriate place in your xmonad.hs file, and restart xmonad:

-- @@@@@@@@ HAAAAAAAAAACK
setWorkArea :: X ()
setWorkArea = withDisplay $ \dpy -> do
    a <- getAtom "_NET_WORKAREA"
    c <- getAtom "CARDINAL"
    r <- asks theRoot
    io $ changeProperty32 dpy r a c propModeReplace (concat $ replicate (length myWorkspaces) [0, 26, 3840, 1028])