Xmonad: 構成で定義したワークスペースで一部のアプリケーションを起動できない

これは私のxmonad設定の一部です。~/.xmonad/xmonad.hs

myWorkspaces            :: [String]
myWorkspaces            = clickable . (map dzenEscape) $ ["web","doc","ssh","devel","chat","temp"]

  where clickable l     = [ "^ca(1,xdotool key super+" ++ show (n) ++ ")" ++ ws ++ "^ca()" |
                            (i,ws) <- zip [1..] l,
                            let n = i ]


    myManageHook = composeAll
    [ className =? "MPlayer"        --> doFloat
    , className =? "Vlc"            --> doFloat
    , className =? "Gimp"           --> doFloat
    , className =? "skype"           --> doF (W.shift (myWorkspaces !! 4))
    , className =? "Mail"           --> doF (W.shift (myWorkspaces !! 4))
--    , className =? "XCalc"          --> doFloat
    , className =? "Firefox"       --> doF (W.shift (myWorkspaces !! 0)) -- send to ws 0
--    , className =? "Nautilus"       --> doF (W.shift (myWorkspaces !! 5)) -- send to ws 5
    , className =? "gvim"       --> doF (W.shift (myWorkspaces !! 1)) -- send to ws 1
--    , className =? "Terminal"       --> doF (W.shift (myWorkspaces !! 3)) -- send to ws 3
    , className =? "Gimp"           --> doF (W.shift (myWorkspaces !! 1)) -- send to ws 1
    , className =? "Codeblocks"      --> doF (W.shift (myWorkspaces !! 3)) -- send to ws 3
    , className =? "stalonetray"    --> doIgnore
    ]

問題はFirefoxやCodeblocksが目的のワークスペースで実行されますが、SkypeとMail（Thunderbird）はこれらの設定に従わずに常にアクティブなワークスペースで実行されることです。