[Evolution] Strange editing bug in 3.20

[Patrick O'Callaghan <poc usb ve>]

I'm seeing a weird effect in 3.20: a strange flashing of the composer
window when I delete text. My usual fixed-width font switches to
something else and then immediately back again. It appears to be a
variable-width font but the switch is so fast it's hard to be sure.
It's hard to explain but very disconcerting as the text and cursor jump
around with each font change (since they are different widths).

Does anyone else see this? I'm using Evo 3.30.3 in Fedora 24 under KDE,
so possibly it's a side-effect of some font choice elsewhere.

poc