Thanks for the test case much appreciated.
I can confirm your issue that setting a "Vertical Stacked Regions (VBOX)" layout on a window causes the reported behaviour.
The workaround is to create a nested "Vertical Stacked Regions (VBOX)" layout region and use the "Only 1 child region (Fit)" layout on the window e.g.

We have filed a bug report and will look to get this fixed ASAP.