My Apple mouse keeps jumping

My apple mouse often jumps. This primary happens in two different ways.

1) When I select a line of text in a document to copy it or delete it and then release the mouse, it often jumps and selects the wrong text. Often I copy the wrong text and don't realize it until I go and paste it somewhere.

2) The other way this happens is when I go to drop a file into a folder. When I release the mouse to place the file in the folder the mouse jumps and places it in the wrong folder. I misplace files this way and don't often know what folder they went in.

Both the situation's are very frustrating. My mouse speed is set to the third notch under scrolling speed. When I move it down to the second notch under scrolling speed, it moves way too slow.

This only happens with the Apple Bluetooth "magic" mouse. It did not happen when I used another mouse.

Pat