Label Based Menu Colouring bug?

I add the Label Based menu to the canvas. Change the Label size to 20. Change the colour of the labels from default to a white background. Preview. All the labels revert to small font again. Exit preview and they are large.

This makes it impossible to use the label based menu with other colours.

I'm using the Phase theme and version 5.4.0

I need to use an alert selector in which the value is not based on the actual number being shown but another number. It looks like the grid does not allow this - so I'm left with the Label based menu which now has this colour bug...