Really didn't know if I would explain right so I added a video to complement. I think this problem is not new.
Imagine a task and subtask. Subtask with category "cat" and parent task with no category or different than "cat"
If that subtask with category "cat" is complete and I filter to show category "cat" it shows the parent also. Its OK. But if I also filter to hide complete tasks then the subtask, which is complete, is correctly hidden but the parent remains showint even though its not the same category as the filtered one "cat". It should not show up.