Hello,
When using filters, when an option has no results, it becomes disabled, but remains selected. This means that it's impossible to remove it, but that it still affects the query and the products being returned and can easily lead the user to make a combination of selections that results in no results returned.
It's probably easier to understand with the screen recording:
https://www.screencast.com/t/QHEe3xs5tvHq
This seems like bad UI to me. A user de-selects a filter - which is supposed to widen the results - and instead suddenly gets a page with no results and no option to undo his last change. They have no option but to open the Product List again and start over... and because they probably don't even understand what happened, they might just go on to do exactly the same mistake again, easily becoming frustrated.
I think once a facet becomes disabled, it shouldn't stay selected and the paramenter should be removed from the query.
Regards