pretty weird issue, essentially not replicable with certainty. Several offending buttons are located on top of a tab control's header (not as a tab page child, they are child to the same surface that tab control is child to) in upper right corner, to the right of the righmost page header button. Usually they are fine, but sometimes all these buttons are only visible as button shapes without text. But when I move mouse to them to click, with the mouse over them the text becomes and stays visible.
To be clear, the buttons are always visible and so are certainly "on top of" the tab control in the z order.
What gives?
We have already seen this issue and it is registered in the support center at:
SimpleButton's Text is not visible
We will research why the problem appears and fix it.