The issue with your Keystone Montana RV roller shade not locking and slowly rolling back up is typically caused by a worn or broken auto-stop mechanism inside the shade. This component is responsible for holding the shade in place at your desired position. For most RV roller shades, including those on Keystone Montana models, the recommended repair is to replace the auto-stop part. We offer premium slow-rise auto-stop components in 1.25" and 1" sizes designed to fit common Irvine and Valu-Line roller shades. Please check your shade’s dimensions and type to select the correct size. If the part you ordered (order 10017922) did not resolve the problem, it may not have been the correct auto-stop component for your shade. We suggest reviewing your shade’s measurements and contacting us for assistance identifying the right replacement part. You can also browse our selection of RV shade parts online to find compatible auto-stop replacements. Replacing this mechanism should restore the locking function and prevent the shade from rolling up on its own.