Hi there,
I made a thread just like this a fair while ago I believe and just noticed this is still not fixed and is still bugging me ocasionally.
Load up a sample, add filter to the/a track, set filter so that its noticeble, “Process Track DSP’s”, delete filter, play sample again.
I’m having this problem the most with the Butterworth 8n filter. I want to get rid of some low rumble but after the processing twice as much lowend is gone.
This could happen if you do the DSP processing and then play the sample on the same track where the DSP device is. Then you’d have the processed result going through the same DSP unit again which will apply the effect again. I’ve caught myself doing this sometimes so may be this is what you’re doing too? Playing with the Enter key instead of the note keyboard should bypass things (unless you’ve put the effects on the master track, I think).
That’s not it 
Could you post a small example song to demonstrate the problem?
You sure it’s not the Track Headroom making you think it sounds less bright because it’s not as loud? That is generally what similar reports hve turned out to be in the past after investigation…