Ian Clowes wrote:

After a bit of analysis I worked out it was because I used the mouse
right next to the window. On sunny days the light was strong enough
to penetrate the case and confuse the opto sensors. A new mouse with
a darker plastic case fixed it.

I found that once a few years ago with a mouse - it only moved up and
down on sunny days! The solution was to take the lid off it and colour
the inside with a permenent marker pen - put it all back together and it
worked fine after that!

--
Cheers,

John.

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