Opponent times out after around 5th move

[Dave Neve]

Hello
Suddenly, I have a strange problem with Winboard
Playing a normal game with me as white against an engine (not online) and with time set at 60 seconds per move, black runs out of time after the 5th move approx.
Just after black runs out of time and I'm invited to save the game, I hear a move sound and black now makes a move (although the clock has clearly run out). The clock starts to run down again for me (white) but I can no longer move anything. The game is indeed over but with a bug of some sort. Happens every time now.
Until this week, I have not had any such problem.
What gives please?
Thanks