Is this a BUG REPORT or FEATURE REQUEST? (choose one):
Documentation request.

Description

During the commit phase the ABCI proxy app returns the "app_hash" to Tendermint. It unclear from the docs how tendermint uses this app hash apart from re-syncing/re-playing the blocks on the ABCI proxy app. More specifically, is it necessary that each node return the same app hash for a given block B1.

Consider the following scenario

Consider a sitatution where the network wishes to upgrade their ABCI proxy app from v1.0 to v2.0 wherein for a given block B1 the v1.0 returns a different app hash as compared to v2.0. So, different nodes might return a different app hash depending on their ABCI proxy app version (i.e. v1.0 or v2.0)

It is unclear as to how Tendermint will behave under such a circumstance?

NOTE: If I have missed some documentation kindly point me towards the same.