When expanding a note editor in the timeline by double-clicking a note region and then undoing the action, the note editor won't collapse. It is necessary to single-click any region, including the expanded one, to update the timeline display and close the note editor. As far as I can see, this problem affects exclusively note editors and not automation or audio editors. Also, the bug only appears when trying to close the editor through Undo. Double-clicking an expanded note region or clicking the inline editor icon work as expected.

Steps to reproduce:

Create a new project, drag a synth to the desktop and create a note track and note region for it in the timeline.

Double-click the note region to expand it and show the note editor.

Click the Undo icon or press Ctrl-U. The piano roll on the track list vanishes but the note editor remains open.

Click any region on the timeline. The timeline display updates and the open note editor vanishes.

Chrome 73.0.3683.75 official build, 64 bits, Linux Ubuntu 18.04.2 LTS