Ok, that's the complete opposite of what I see. Can you send me your settings and test audio?
Ok, issue confirmed. And I know the cause: "BAD!" was designed to improved IMD for bass tones, which is at least 95% of all the bass in music, and it works very well on that. But on random bass (bass noise, basically), it makes things slightly worse. (The improvements on bass tones is still much bigger than the detrimental effect on bass noise). I'll see what I can do to improve this, but even with this, you really should still keep it turned on for music.
I think I found a good compromise for the behavior. I've added a setting for it ("Allow distortion on thunder bass (threshold)"), which I'm going to hide in Extreme Tweaker mode. Basically, we do indeed want this filter ("BAD!") to be active on bass tones and not on bass noise ("thunder"), because in the latter case the IMD that's caused by this filter is actually worse than the IMD it's cleaning up. It looks like highs IMD is mainly annoying when it has a pattern in it. "0" is equal to the old behavior, "50" (the maximum) is getting close to turning "BAD!" off. 30 seems to be a good compromise, I haven't been able to detect any added distortion in music so far and the distortion added to pink noise is largely gone. With higher values (50) I do have the impression that there's more distortion - I haven't done a blind test though. The default is currently set to 25, 30 is probably better but I think the risk of adding IMD in music is bigger than any gains from this filter, so without testing a lot more I want to err on the safe side.
On average, a bit more highs get through with this setting > 0 (nearly no effect on other frequencies), which is probably a good thing as long as those extra highs aren't distorted.
I'll run a new build tonight.
Edit: At 50 there's clearly more distortion. 25, 30 and 35 seem to be ok. I'm not too sure when I test it (even in a loop, I think I hear different things every time even with the same settings), but I measured it and - at least for the music that I tested with, 35 seems to be still ok. 50 clearly isn't, both based on listening tests and measurements.