Hi I try to replicate this issue for I have it my self for many year, but perhaps I found a solutions. If you hit the Catch Playhead button you find three options, unmark those both in Arrange and Pianoroll windows and in the Preference Settings. When I did so all work as it should do, zoom and pianoroll stand still for editing. I working with Logic 10.4.8 and 10.5. I don't have tested 10.5 yet!