transpose midi tracks in GarageBand 10.4.12

I have multiple tracks, each one with either a MIDI loop or a MIDI instrument. When I select a region -- any region, or all of them -- and move the Transpose slider to 2 (or any other value) the region will show "+2 semitones" (or other value) but it doesn't sound any different. Ditto with the Transpose Track. The Score reflects the changes; Piano Roll does not.

If I use the Control for AUNewPitch, I can make it change pitch, but not with the Transpose slider or Track.

Why is this?

Thank you.