I've put up with the same warnings for a while now on my Mandrake 7.1 box. After reading this post, I did a little poking around and it seems that Term::ReadLine::Perl::readline has a few problems parsing inputrc files. It does case-sensitive comparisons for the values 'On' and 'Off', and doesn't like trailing comments (this from looking at the code and experimenting with moving the trailing comments to separate lines).

The easiest fix is to install Term::ReadLine::Gnu which parses Mandrake's /etc/inputrc without any problems. I haven't looked at the latest version of Term::ReadLine::Perl to see if these problems have been fixed or not. If I can find time, I may try to work up some modifications and submit them to the maintainer.