[Evolution] Mark-as-Read not working on subfolders

[Douglas Summers <ajgringo619 hotmail com>]

Running Evolution 3.34.2 (by Flathub.org)

I recently upgraded to the aformentioned version as the stock version
(3.28.5) that comes with Mint 19.2 was having issues with white-on-
white text with dark themes. Now I'm having a minor issue when I try to
mark folder(s) and their subfolders as read; one folder at a time works
as expected, but the subfolders are ignored. This was working on
v3.28.5.