Yes, I think that makes sense.
Basically then, consider that I wanted to modify buttons in the top row and then eventually show the top row only as my default configuration.
To preserve all subsequent rows for the possibility that I may want to reinstate them at some time, the best strategy would be to first display all rows, then modify the top row as required, close the Button Editor, and then use the Core Settings panel to change the display.
This would change the configuration and preserve the setting for all four rows. Any subsequent change of the button display to show just the one row would retain details of all buttons behind the scenes.
So, I agree with you - not a bug, perhaps more a case of the end user being aware of the consequences.
At least I have found out how the blank rows were caused, and, as a result of your earlier post, been made aware of how easy it is to create, and recreate the default display.
Many thanks for your patience.