Zoom doesn't work in Notation view of MIDI editor pane

[dmitch]

When I display the MIDI editor pane in the Edit window (via View > Other Displays > MIDI Editor) and enable Notation view (via the button with the pair of sixteenth notes), the Zoom tool just acts like the Selection tool. A single click is supposed to zoom in (per the manual); it does nothing. A Marquee selection using the Zoom tool is supposed to zoom to the selection. Instead it just results in a marquee being selected. Even the cursor, when Zoom tool is selected, looks like a Selection cursor - not the magnifying glass normally used by the Zoom tool.Doesn't matter which Zoom tool is selected (single or normal); both behave the same.

Oddly, in the separate Score editor window, which AFAICT is supposed to act pretty much exactly the same as the Edit window's notation view described above, the Zoom tool works fine. Correct cursor; one click zooms in around the click; marquee selection zooms to the selection.

Any hints or ideas as to what I might be doing wrong?

PT 2020.5.0. 2019 iMac running macOS 10.15.5.

Thanks.