[Haskell-cafe] unexpected behavior from filterM doesFileExist =<< getDirectoryContents

Can somebody explain this?

getDirectoryContents inD

["..","#sanity.txt#",".","sanity.txt","etc.txt","patchTagDir.txt","jail.txt","notjail.txt","alldata.txt","allobjs.txt","namesNSizes.txt"]

filterM doesFileExist =<< getDirectoryContents inD

["sanity.txt"]