QDateEdit display bug on popup opening

hello,

i upgraded from 5.12.3 to 5.12.4 and have discovered that QDateEdit's popup stays blank or is rendered incompletely after the second opening.

Qt 5.12.4 + PySide2 5.12.4 --> problem occurs
Qt 5.12.4 + PySide2 5.12.3 --> no problem

so it must be related to PySide2 in my opinion. see attached screenshots.

i can reproduce the error every time: click on arrow, clicking away or selecting date, reclicking arrow --> stays blank.

also tried latest pyside2 snapshot, no difference.

using macOS 10.13.6 with Python 3.6.8

cheers