It "just" fails because UPX fails even though it is installed. Apparently it doesn't support all platforms Debian supports. Nevertheless there are attempts to get upstream to remove the requirement on UPX or at least make it easy to disable.
Reegards, Remko Bijker -- To UNSUBSCRIBE, email to debian-bugs-rc-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org