Thanks Fred,
It's the Magic Mouse. It's just like you say; the latch doesn't want to catch. I h ave to push hard and it usually catches but not always. I didn't realize different brands of batteries might be different diameters but it makes sense. Quality control rarely goes beyond 1 decimal place. Interestingly, this usually happens after a battery change. But then gets better and resolves without changing the batteries. I suspect sooner or later I close it "just right" and it's fine until next battery change. Irritating.
Went for first sail of season today. Cold and 20k wind. What could go wrong did go wrong; typical first sail. Enjoyed!
Geoff