Vertical keyboard missing in MIDI key editor

Hello! This is a bit of an odd bug. I double-clicked on a MIDI part to open the editor on my secondary monitor which opened in the default non-maximized size. I maximized it, then un-maximized it to that I could set a custom size. When I did this, the keyboard roll disappeard:
When I maximize the window, it reappears:
Un-maximizing causes it to disappear again, in an endless cycle.