I just migrated our PB application from PB 12.5 to PB 15. When I tested the client, the cells in (several) Grid Datawindow(s) appear in black color, thus hiding the text (I vaguely remember seeing something like this in an old version of PB). I just noticed this happens even in Freeform datawindow on top. (may be edit masks?).
I have not attempted any further testing nor any Datawindow fixes or workaround yet. I am running PB 15 Beta on Windows 7 x64. This did not happen in PB 12.5 which I migrated to recently.