I observed similar behaviour.
Two pools. Pool A composed of two hosts. Pool B is single-host. B runs a VM with XO from source. Two VMs on host A1 (on local SR), one VM on host B1 (on local SR).
Host A2 has a second local SR (separate physical disc) used as the target for a CR job.
CR job would back up all four VMs to the second local SR on host A2.
The behaviour observed was that, although the VM on B would be backed up (as expected) as a single VM with multiple snapshots (up to the 'replication retention'), the three other VMs on the same pool as the target SR would see a new full VM created for each run of the CR job. That rather quickly filled up the target SR.
I noticed the situation was corrected by a commit on or about the same date reported by @ph7.
Incidentally, whatever broke this, and subsequently corrected it, appears to have corrected another issue I reported here. I never got a satisfactory answer regarding that question. Questions were raised about the stability of my test environment, even though I could easily reproduce it with a completely fresh install.
Thanks for the work!