Main window stays dim after dismising the recover backup window

Hi, I got this minor inconvenience or quirk.
Not sure if it’s something about my system. I didn’t see it mentioned here nor in the github issue tracker.

Description

After closing the window to recover a backup file, the main window stays dimmed when regaining focus.

When launching MyPaint, if there’s a backup from a previous crashed session, the recover window opens.

If I either dismiss (with the close button, or with the “Decide Later” button), or if I delete the backup and close, the main window remains dim as if it was out of focus.

It goes away when I hide/unhide (minimizing and restoring), or if I open another modal window from MyPaint (the About window works fine).

Basic System Details

Stable appImage v2.0.1 2.0.1+git.478280f

Operating System + Version:

Linux, OpenSUSE Leap 15.2, KDE Plasma 5.18

Note: seems unrelated to Plasma’s desktop effects.
Only Gtk apps do this dimming effect for modal windows with my current settings.
Enabling/disabling “Dim Inactive” in Desktop effects only adds/removes a second dim effect on top.
I even had Dim effect disabled when I found this quirk.

How to Reproduce

1 - Start MyPaint, draw something, and kill the app. A backup should be generated.
2 - Relaunch the app. Starting it from Dolphin or shell does the same thing.
3- If the recover window doesn’t show automatically, open it from File menu → “Recover file from an automated backup…”.
4 - Close the window by either the close button, or the “Decide Later” button. Deleting the backup before closing makes no difference.

If I chose to save and open instead, it works as expected.

Workaround:

Minimize and restore, or open the About dialog (or some other modal window) and close it.

Has anyone else had this happen? Is it something known?
Is there some way to disable the dim effect globally on Gtk apps?