Goto [[w:de:Spezial:Missbrauchsfilter/test]], use rule #17 with "changes by user" = 188.8.131.52.
This will trigger some edits.
Now add the line
| (rcount("something",added_lines) < rcount("something",removed_lines))
somewhere in the rule. Then it will fail.
Maybe there is a maxmum length of filter rules?
(Filter rule #3 at w:de was very long (> 1000 chars). A work-around was to move a part of the rule to #17.)