Today I was fooled by Veam backup

I installed a VM "NEW" to replace an older VM "OLD".
I didn't want to lose the history in my backup job of OLD so I moved my newly installed vmdk files from NEW to OLD.
So I would keep the OLD VM with its UUID but with my NEW vmdk.
So I thought the backup job OLD would continue working by backuping the NEW vmdk now.
I was wrong as Veeam backed up the OLD vmdk that I moved elsewhere in my datastore!

I tend to think it's a bug in Veeam. I mean, I ask the software to backup a VM, whatever it is made of.
Why doesn't it "ask" VMware which disks is set up in this VM and acts accordingly?
Now let's give it another try.
I edited my backup job and selected "SCSI 0:0" instead of "All disks". This is a lowlevel definition of the vmdk and it is also called SCSI 0:0 in the VM. So this should work but it doesn't. Veeam stills backup the wrong vmdk.
What's you thought on this? Bug or misunderstanding from my side?