Could be finding another 'echo' and 'copy' - executables of the same name, for instance. Insertion of a shell metacharacter can be sufficient to force use of the shell commands. Try, eg:

$ret = `echo dog <NUL`;
$ret=`copy c:\\perl_test\\test.sas c:\\perl_test\\test_new.sas <NUL`;
[download]

and see if that reinstates expected behaviour.

Cheers,
Rob