Bug, or me being stupid?

I want to copy a dir, preserving modes and timestamps but assuming 
ownership, and I keep getting this error:

daedalus@bob daedalus $ cp -r --preserve=mode,timestamps fly fly2
cp: ambiguous argument `' for `--preserve'
Valid arguments are:
   - `mode'
   - `timestamps'
   - `ownership'
   - `links'
   - `all'
Try `cp --help' for more information.


Am I being stupid, or is this a bug? I'm using coreutils-4.5.3.

Andrew Walrond