Program editing crash

[Boo]

Have twice now had the calculator crash/lockup when editing a program. Only thing I could do to recover was hard reset. When crashed, editor view is OK, but no scrolling, no interaction or ESC or anything. Soft keys on screen don't work, but the battery-saving brightness dim does come back to full bright on keypress. Very frustrating.
Original firmware, as I still haven't managed to update yet.