BaseDistributionInterceptor.primaryReturnHandler() doesn't replicate writes to the backups if cacheConfiguration.clustering().hash().numOwners() == 1. That check is incorrect, because a segment can have more owners than configured:
1. In a replicated cache, the configured numOwners is ignored, and all the members are owners.
1. Even in a distributed cache, during rebalance, the segments being moved will have more than numOwners owners.