Find rules: Incorrect behavior for selected set after changing group

[mttsch]

Select a group and a set:

Change the group:

Note that the set also changed (visually) in the dropdown, but the parameter in the URL remains the same. The result list is, incorrectly, empty.

Select another set and then change back to the set from the previous screenshot:

Now, the rule result list is not empty (different rule count in set dropdown and result list is caused by #3214).