Duplicate MAC address in VMware deploying from template

I am trying to deploy a VM from a template. This template has been used dozens of times before; nothing special. The problem is that seemingly out of nowhere when I deploy a VM, it's giving it the same MAC address as an existing powered on VM.

Both VMs are using automatic MAC assignment.

It seems that the usual cause for this is having more than 1 vCenter without giving each one a unique ID. Thing is, we only have 1 vCenter.

I have confirmed in the vCenter database, using the following query, that there are no other conflicts in the cluster:

SELECT TOP 1000 
      [MAC_ADDRESS],
      COUNT([MAC_ADDRESS])
  FROM [VIM_VCDB].[dbo].[VPX_NIC]
  GROUP BY MAC_ADDRESS
  HAVING COUNT([MAC_ADDRESS]) > 1

I keep deleting the newly minted VM and trying to re-deploy it, but it gives out the same MAC every time.

When I create a new VM from scratch, it uses a unique MAC.

I can't find any other instances of something like this online, and I can't figure out how this is possible nor what I can do to fix it. I don't want to start assigning MAC addresses manually.

Update

This has gone from a problem that was repeatable to.. not a problem. I don't know what happened or why, but this originally occurred for me on Friday evening, several times. I was able to repeat it this morning before posting this.

Testing now shows unique MACs being generated; no duplicates.

I have no idea why, I'd still like insight if anyone has ideas. I have a sneaking suspicion that this is going to come back. Ugggh.