If you are in kanban board view (e.g. by tags) and add a subcategory filter, instead of filtering the kanban board by the subcategory, you are redirected to latest view instead. If you go back to the board afterwards, the subcategory filter is dropped.
It would be nice to change this behavior, but not a bug per se.
However, if you are in kanban board view and add a tag filter, instead of filtering the kanban board by tags, you are also redirected to latest view.
If you go back to the board aftewards, the tag filter is kept.
This behavior is certainly buggy. Either stay in board view to begin with (preferred) or do not support filtering boards by tag in the first place.