I’ve been using openSUSE for quite some time now, but this is definitely the first time that I’ve noticed this ( though probably because I tend to use zypper or the 1-click install rather than entering YaST).
zypper lr -u
zypper se -s -i -t pattern
zypper sl -d
Edit 2: Andreas Jaegar comments on the above:
Found it: The pattern is part of Mono Community pattern. As these ymp-patterns have no category, the software manager picks a pretty much random order. And it happens to be under proprietary software in this case.