When duplicate sources and the --backup option are provided to cp, GNU cp skips the duplicate source check and proceeds with copying the files. However, uu-cp does not currently behave this way.

For example

touch a; mkdir d;
cp --backup a a d/ 

GNU's cp would skip duplicate source check and tries to overwrite the "just-created" file and give us the error, (if backup--numbered is given then this won't file).

cp: will not overwrite just-created 'd/a' with 'a'

While uu-cp would give us

cp: warning: source file 'a' specified more than once