I always wonder if it's some odd thing going on in the DAW.
Would you be willing to export that track as two tracks--one with drums and one with synth? Then listen to them solo, then run them together (with WAV files instead of instrumentation)? Would be neat to have that illusion confirmed rather than it being a DAW artifact.
My setup's DAWless (this was two synths and a drum machine plugged directly into a mixer that was outputting to speakers) and I didn't end up making any records of this session, so I can't provide WAVs, but I can rule out DAW artifacts :)
Would you be willing to export that track as two tracks--one with drums and one with synth? Then listen to them solo, then run them together (with WAV files instead of instrumentation)? Would be neat to have that illusion confirmed rather than it being a DAW artifact.