More Filter Problems - Weird Gain/Distortion/Bass problem

I've re-created this both with my UMCP2 and with my controller disconnected and just using my mouse.
I play a track, start turning the filter from central to the right. Then I slowly turn the filter back to the left until it is central and no filter is applied - no light is on next to the filter dial.
At this point the track appears to be louder/bassier. If I click the turn filter light to switch it off completely, the track stays the same. On headphones the track is borderline distorting.
I've attached a screenshot of a track I recorded opened in Audacity to show the waveform. The highlighted area is where I turned the filter. Before and after are pretty much the same pattern, but notice more blue and the higher peaks on the right-hand side where the extra volume/bass is in place.
UPDATE: Described the problem better.
I play a track, start turning the filter from central to the right. Then I slowly turn the filter back to the left until it is central and no filter is applied - no light is on next to the filter dial.
At this point the track appears to be louder/bassier. If I click the turn filter light to switch it off completely, the track stays the same. On headphones the track is borderline distorting.
I've attached a screenshot of a track I recorded opened in Audacity to show the waveform. The highlighted area is where I turned the filter. Before and after are pretty much the same pattern, but notice more blue and the higher peaks on the right-hand side where the extra volume/bass is in place.
UPDATE: Described the problem better.