That is not a bug. You should be using Musical timebase as that will respond to changes in the tempo track. That's what musical timebase is a way for tracks to musically or rhythmically follow the changes in a project.

Musical timebase does not restrict you to quantize values unless you have turned on Auto Quantize when playing, or have snapping on when editing. The locators are synced to time, so they will stay on say bars 2-4, if that's where they were before the tempo was changed.