QComboBox shown with black popup background

When displaying a QComboBox inside a QScrollArea, the background of the combobox popup is displayed in black, rather than white.

6.6.2

6.7.0 RC1

Only occurs on Windows, using windows11 or windowsvista styles. Fusion or Windows styles are not affected.

I have attached a simple demonstration of the problem.

Note: the problem can be mitigated by setting a style sheet for the combobox, e.g.:
    a.setStyleSheet("QComboBox QAbstractItemView {background-color: red}");

gives you: