User writes:

“I agree, I would expect that adding a different filter to the first position would override whatever's already in that position (e.g. the 'answered no to question x' in my example).

The part that is unexpected as a user is that the filter dropdown menu behaves sometimes like the position of filters is important and sometimes like it isn't. For example, changing dropdown 2 when there is already a filter 1 will change filter 2, but changing dropdown 2 when there isn't a filter 1 will change filter 1. If I use dropdown 2 twice in a row, I can get a different result (changing filter 1 then changing filter 2), however if I used the first dropdown twice in a row, it would always change filter 1.

In computer speak I would expect this operation to be idempotent i.e. doing something in dropdown 2 would always change filter position 2.“

Ultimately, the user us using for a different user interface to remove and add filters to multiple tables.