Hi all! Pumps2 (and anyone else experiencing this issue) - on the mixer, are your "this song" and "all songs" faders set higher than zero? That's the only way I was able to duplicate this issue.
"This song" and "All songs" were both left at zero.
Please note the problem went away when I did an options reset of "most". Any theories of what might explain that (just idle curiosity)? Are there any options that affect how mono tracks are rendered versus stereo tracks?