During entry of new fact, the fact entry box goes black except for the line I am typing on

Several times over the last couple of days, as I am typing in a fact (typically a birth, death, or marriage date), the entry lines (date, place, proof, etc.) all go black except the line I am typing on. In order to finish entering, I have to close fact box and re-open to finish. I cannot repeat the problem, it just suddenly occurs. I could not find this topic mentioned anywhere else.