Qt Designer: Items just added to scratch pad are not visible on Windows

Note: bug affects Windows only (worked on Linux). Tested on Qt Creator 9.0.1 built with Qt 6.4.0.

Sequence:

1. Open a .ui file in Design mode (I used the Calculator Form Example project).
2. Drag a widget from the form to the widget box on the left to add it to the scratch pad. The first widget shows up just fine.
3. Drag a second widget to the scratch pad.

Issue: the second widget is not visible.

Here is a screenshot. There should be two items in the Scratchpad currently:

Workaround is to collapse and expand the Scratchpad box. After that the second widget becomes visible as well: