To reproduce this bug:
- Load a DrumSynth.
- Turn the [01.Volume] and [04.Bass volume] up to the maximum. (Lower the main volume.)
- Play a bass drum note (like C1).
- Move either [02.Panning] or [0D.Bass panning] one little click to the left, so from 0 (4000) to -1 (3f80).
- Play the same note.
Panning values around 2000 and 6000 give centered stereo and at the far ends it's one channel again.
Volume values between 4000 and 8000 give something in between: bias to the L or R side.
And on top of this (at these high levels) the L and R channels seem to have the opposite phase.
The same happens with the hi-hat and snare sections.