At some point after approximately 30 minutes, the left/right and up/down
arrows on the scrollbars in MailView changed from arrows to the numeric
characters 3/4 and 5/6 respectively. This was consistent. All up arrows
were labeled "3", all down arrows "4" etc.

The change occured when a dialog that was obscuring these scrollbars was
dismissed, exposing them (a redraw occurred).