Z: K&R's strcpy is broken, e.g., you can forget to null-terminate the string. Mine is safer.
Ohters: It's not broken, of course it'll do something unpredictable if you break its preconditions.
Z: strcpy is still broken.
Others: Your function will break too if you pass it the wrong length.
Z: This cannot happen, K&R strcpy is broken, mine is safe.