Just FYI:

I have a laptop these days.

I've had similar problems with the cursor coming and going in the middle of my sentences as I type. It's nothing to do with the mouse in my case, it's more the place I rest my left wrist on as I'm typing. Bottom left hand corner of my laptop. When I don't do that, it doesn't happen. If my wrist gets heavy there it will take the cursor off into some other place in my text that I'm typing.

Weird but true.