Hi Devek
Try this and let us know how it goes:
- In the Finder, go to (your user account) ~> Library ~> Preferences
- Move the file com.apple.driver.AppleBluetoothMultitouch.mouse.pl ist to the Trash
- Move the file com.apple.driver.AppleHIDMouse.plist to the Trash
- DO NOT empty the Trash
- Restart your computer
- Set the scroll speed
- Restart your computer and use it for awhile
If you continue to have problems with your Magic Mouse, put the files you trashed back where they came from.
Otherwise, you will have either fixed the problem or eliminated the two preference files above as the source of your problem.