Strange palette behaviour in Qt widgets for Linux (6.5.2 & 6.6.0)

When running a 6.5.2 or 6.6.0 widget application under Ubuntu 22.04/23.04, certain widgets experience a temporary palette change when focus shifts to a secondary window (e.g. modal dialog).

Issue also manifests whilst dragging the window around the desktop.

Issue appears to affect both fusion and non-fusion style, though actively selecting "fusion" style doesn't appear to do a lot per se (is GTK+ the default for Linux)?

TabWidgets, scrollbars and buttons are particularly affected.

Please see attached images for clarification.

Note: issue was not present in 6.4.3.