It's a matter that has everyone stumped at the Cricket World Cup: Why aren't the bails coming off when the ball hits the wickets?

There were five instances in the first 13 matches of the tournament when the electronic "Zing" bails lit up after being struck but failed to drop from the wickets.

Players are unhappy . Spectators and pundits are bemused. The makers of the bails don't understand the glitches, either.

"Nothing has changed with the Zing system for years," David Ligertwood, director of Zing, said in emailed comments.

"The Zing wicket system has operated in well over a thousand games and this issue has not happened frequently."

Ligertwood said Zing is "currently monitoring the situation" and "reviewing all aspects and at the same time looking into whether there are some practical modifications that can be made in the future to make the bails come off easier."

He said there were "competing interests" that need to be balanced in context.

"For example, the game doesn't want the bails coming off too easily," he said. "This issue is obviously important as the game wants batsmen being dismissed when they should be.  But even with this unusual spate of bails not falling it remains definitive and it remains the same for both sides."

The International Cricket Council defended the zing bails, saying the plastic version that contain LED componentry are actually lighter than regular wooden bails.

Zing bails have been in use since 2012, and featured in the last World Cup in 2015. They help to identify run-outs and stumpings.

The most recent incident happened in the match between India and Australia, when Australia batsman David Warner glanced a delivery by Jasprit Bumrah off his bat, onto his boot and onto the base of the leg stump. The flashing bails lit up but weren't dislodged from the grooves at the top of the wickets. That meant he was not out.

Similar occurrences have also taken place in the following matches: England vs. South Africa, New Zealand vs. Sri Lanka, Australia vs. West Indies, and England vs. Bangladesh.

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