If you expand a collapsed filter and choose a filter, it re-collapses; the filter should remain expanded. I'm stumbled upon this by:
1. Search for "use title summary"
2. SUB-AREA is collapsed, expand it and click on one of the filters
The results are filtered correctly, but SUB-AREA re-collapses. I think it should remain expanded and only re-collapse when none of its filters are selected.