I am not sure this is a bug, but I also don't think I am doing this wrong:
I use the "Map - Region" or "Map - County" to find those we did not have find in yet or to see how many finds in each subdivision.
Seems to work.
I can add a filter "Type: only multi checked" and then have to set "Size: all 7 checked", which is easy to do.
The result however does not change. I would have expected to now only see Multichaches (and a lot more red and smaller numbers). The map and number breakdown does not change though.