QML TextField does not accept Greek annotatation letters in QQuickWidget on X11

When one uses the Greek keyboard layout, the QML TextField component in QQuickWidget does not accept annotation letters like ά, ό, ί, ύ when typed as ';α', etc. (the semicolon is used as a modifier for the following character - so just typing α should get you just α, and typing ;α should get you the accented version ά).

The TextField correctly shows these characters when they are copied from somewhere else, it just does not allow typing them.

This does not happen with the QQuickView.

This bug was originally reported to KDE's bugzilla:
https://bugs.kde.org/show_bug.cgi?id=370908

I've attached a minimal example which can be used for testing this issue.