PL4 Menu Items disappear when used with Adobe Bridge

I’m using Adobe Bridge V11.1 with PL4 V4.3 v4580 on Win 10 PC.
PL4 is set as the External Editor in Bridge preferences.
Double clicking an image in Bridge starts PL4 and the image is displayed.
At this point, a problem arises.

It is not possible to select any of the menu actions in PL4, because the drop-down menu lists cannot be selected.
They disappear from view when the mouse pointer hovers over them.
The same problem happens if I right-click on the image. The context menu list appears but it disappears if the pointer is moved over it.

There is a work-around rather than a solution.
If I start PL4 before any image is selected in Bridge, the PL4 menu functions work as expected.

This behavior is only observed with a Bridge/PL4 combination and if PL4 is not already running.

The problem is probably caused by Adobe Bridge and not PL4, as I have used other file managers and DAMs and the issue does not occur.

I know this is not a huge problem but rather an inconvenience. However has anyone else noticed this and better still, has anyone discovered why and how to fix it?