The tuning of the portamentos in the melodies (starting at 0:30) of the attached song often go sharp of the target note. This issue has stumped me since '99 because it has played back differently in almost every player outside of IT. Best guess is that it is related to the Amiga pitch slides setting (in F12 settings), possibly combined with the high octave used for leads. It almost seems to go proportionally sharper with higher notes.

I recently tested this issue in Schism 20190801, ModPlug Player 1.46.02, XMPlay 3.8.4, and foo_openmpt54 0.5.0. Most players sounded similarly out of tune with only XMPlay getting close to IT.

The attachment includes the original IT file as well as a short clip with accurate pitch rendered using IT 2.14's stereo WAV writer.