Qt WebEngine subpixel antialiasing regression?

[Brendon Higgins <brendon@quantumfurball.net>]

Hi all,

I'm wondering if anyone else is experiencing this: Qt WebEngine text content 
is not getting subpixel antialiasing, even though subpixel antialiasing works 
correctly most other places (including other Qt/KDE widgets). For me I notice 
the problem particularly affects Falkon and KMail in the message pane: in those 
places, all text is antialiased greyscale and not subpixel RGB.

This old QT bug report is related and shows what I mean:
https://bugreports.qt.io/browse/QTBUG-62146
In fact, the test case attached to that report also fails for me - I get 
output like "Qt5.8.0.PNG".

It looks like that regression was once fixed and has now regressed again! 
Unless something's just weird on my install... I'm running Debian Testing with 
Qt 5.15.2 packages installed.

Best,
Brendon