Originally Posted by
Rob P.
If your chain falls off when you roll the bike backwards it would also fall off the cogs when you spin the pedals "backwards" and it DOES NOT DO THIS! If your bike does this then you have maintenance problems that need to be addressed rather than blaming a component that has nothing to do with this.
Such sound and fury, signifying nothing.
Even a pristine drivetrain in perfect alignment can do this if it's cross chained, especially using an 9 or 10 speed drivetrain. Take any new bike from your favorite shop, throw it in the big/big combo and spin the pedals backwards, see what happens. Or, as you go on to suggest, the rear derailleur got moved to a higher cog before rolling backwards.
OR someone hit the shifter while the bike was parked.
Is that a maintenance problem?