Do you experience this behavior only inside of Photoshop Elements? Only when Elements is running? Or always not that you have updated to 9.0.3? Have you tried a wired mouse to see if you experience the same behavior? Have you tried uninstalling Elements to see if the behavior continues? Reinstalled the application without updating? Have you tired updating the software/drivers for your mouse?
When you say double-click works, do you mean you can only double-click on files, menus, etc.? So you cannot use any single-click functions. Or is a double-click required to perform a single-click (triple-click to double-click)?
The 9.0.3 update mainly deals with issues between the Elements interface interacting with Wacom tablet tools. Click vs Double-click shouldn't be effected.