IF the shifting guide pulley is not directly under the same cog the chain is on ,
then pushing the bike backwards turns the whole drivetrain, and derails the chain
between the cog and the guide pulley, tangling up the best otherwise adjusted derailleur mechanism.

Here is what you do , grab the bike's back brake, roll it up on its back wheel ,
do a little pirouette , on the back wheel,
and set the bike back down facing the other way and go Forward with the bike moving forward with you.