In https://ghc.haskell.org/trac/ghc/ticket/5251, GHC trac user Orphi reports:

The copyFile function fails to copy various metadata to do with a file.

(GHC 7.0.2, directory 1.1.0.0 - not that I expect it to matter.)

The cause is simple: Rather than calling an OS-specific "please copy this file" function, the directory package attempts to implement this logic itself. And does it completely wrong.

The fix should be easy; we just need somebody to figure out what the appropriate native OS function is on each platform.