The topic http://infinispan.org/docs/stable/user_guide/user_guide.html#hot_rod_transaction does not mention about the force-return-values on the client configuration.
When it is true, the system will validate the cache version and only one transaction will commit.
When it is false, the system won't validate the cache version and both transactions will commit.

It will be nice to have this behavior documented. Also, an example code for each behavior is welcome:

Here is an example:
A=0 (cache), B=0 (cache)
TX1: write A = 1, write B = 1
TX1: TODO
TX2: TODO
TX1: TODO
TX1: commit
TX2: commit