To what exactly? Most people most of the time attach filters to clips but they can also be added to the track or Output. I will assume clip for now…
At this point the clip that you deleted is removed again and so do the filters on it as well too. That is by design. I do not understand what you expect. In case the filter was added to a track or Output, I do not reproduce it.
I can only apply filters to clips in the timeline. I have no idea about having a filter to a track or output. So you assume correctly.
What do I expect after deleting a clip from the timeline that had a filter? I expect to restore the filter if I redo. This is what redoing means - recovering every step. Otherwise, we deal with data loss which is critical.
As I test it now, it works for me, too. Maybe I did describe an unrelated scenario, id est there was another procedure for this anomaly to appear. I think I didn’t click the clip again after the first redoing and so the filter seemed to have disappeared for me. If I meet it again, I let you know. As for now, the alert’s down.