The mv-command doesn't care that your files are
writeprotected (eg. mode 0444). You are allowed to mv a file
(any mode) onto a writeproted one (thus loosing it). The
rm-command doesn't (as expected) allow you to delete
writeprotected files without either a warning or the f-flag.
This bug was not in RH5.1 (fileutils-3.16-10) and pre. It
seems to have been introduced with v. 4 of fileutils as it
also was in RH6.0 (fileutils-4.0-1).
Fixed in 4.0-19 (rawhide).