I noticed some inconsistencies in how ENOTSUP errors were handled by cp.

$ dd bs=1M count=10 if=/dev/zero of=t.vfat
$ mkfs.vfat t.vfat
$ mkdir m.vfat
$ sudo mount -o loop t.vfat m.vfat
$ ./src/cp --preserve=all a m.vfat/
./src/cp: setting attribute `user.foo' for `user.foo': Permission denied
./src/cp: setting attribute `user.foo2' for `user.foo2': Permission denied
./src/cp: setting attribute `security.capability' for `security.capability': Operation not permitted
./src/cp: preserving permissions for `m.vfat/a': Operation not supported
$ sudo ./src/cp --preserve=all a m.vfat/a
./src/cp: failed to set the security context of `m.vfat/a' to `system_u:object_r:user_home_t:s0': Operation not supported
./src/cp: failed to preserve ownership for `m.vfat/a': Operation not permitted

Notice how one gets "Operation not supported" when the target exists.
The attached should fix it up.

cheers,
Pádraig.