System.FilePath.joinDrive problem

Hello all, The joinDrive function currently produces paths such as "C:File" when calling "C:" "File". This is apparently handled in a special case:

| otherwise = case a of [a1,':'] | isLetter a1 -> a ++ b _ -> a ++ [pathSeparator] ++ b

This seems wrong, as far as I know "C:File" is not a valid path. What is the reason for this special case? In particular this problem results in cabal wanting to install packages to "E:Haskell" on my computer (unless I pass a --prefix flag). Twan