[xmonad] Applications cover xmobar

[Guillaume Thouvenin]

Hello,

I'm new to xmonad and I observe a strange behaviour with the status 
bar. I started xmobar as follow:

in my xmonad.hs I have:

main = do
  xmproc <- spawnPipe "xmobar"
  xmonad $ azertyConfig
    {
      workspaces = myWorkspaces,
      terminal   = myTerminal,
      modMask    = myModMask,
      logHook    = dynamicLogWithPP $ xmobarPP
        {          ppOutput = hPutStrLn xmproc,
          ppTitle = xmobarColor "green" "" . shorten 50
        },
      manageHook = manageDocks <+> myManageHook <+> manageHook azertyConfig
    }

in my .xmobrrc I have:
Config { font = "-misc-fixed-*-*-*-*-10-*-*-*-*-*-*-*"
       , bgColor = "black"
       , fgColor = "grey"
       , position = TopW L 90
       , lowerOnStart = True
       , commands = [ Run Weather "LFLG" ["-t","<station>: 
<tempC>C","-L","18","-H","25","--normal","green","--high","red","--low","lightblue"] 
36000
                    , Run Network "eth0" 
["-L","0","-H","32","--normal","green","--high","red"] 10
                    , Run Cpu 
["-L","3","-H","50","--normal","green","--high","red"] 10
                    , Run Memory ["-t","Mem: <usedratio>%"] 10
                    , Run Swap [] 10
                    , Run Com "uname" ["-s","-r"] "" 36000
                    , Run Date "%a %b %_d %Y %H:%M:%S" "date" 10
                    , Run StdinReader
                    ]
       , sepChar = "%"
       , alignSep = "}{"
       , template = "%StdinReader% }{%cpu% | %memory% * %swap% | %eth0% 
| <fc=#ee9a00>%date%</fc>| %LFLG% | %uname%"
       }

I can see the status bar in a workspace when it is empty but when I 
start an application (xterm, firefox, ...) the application covers the 
status bar and therefore I can not see it. I tried to modify 
lowerOnStart = False but this hides the top of my application. I'm 
using xmonad 0.9.1-2 and xmobar 0.9.2-1 with ubuntu 10.04.

Thanks for your help,
Guillaume