Document window opening very small behind toolbar

When I open a file, the document window sits underneath the (docked) Toolbar.

Sometimes it is so narrow I have to drag it across or selectWindow/Arrange/Tile to see it.

Once they are moved, if I hit Maximise button then it (almost but close enough) fits to the visible space.
This has been a long standing bug for me in both GA and Beta builds. It happened on my previous MacBook and also has on this new MacBook from a clean install.

Almost as annoying as the InDesign bug which is similar but relates to window height.

This happens on both second monitor and also when using Mac on its own.