if your auto shut off uses a solenoid and pressure switch then your water pressure may not be high enough to trigger the shut off. The solenoid valve also has to be installed before the RO membrane. But typical auto shut offs do not use solenoids.
This a typical auto shut off:
Installed like this:
BRS also has a video:
http://www.youtube.com/watch?v=ssa6njb5nV4