Hey Bretty,
Yes actually that is default functionality of vCAC which is predefined into Workflow responsible for post-deployment customization of vApp`s VM. As per my understanding which obviously make sense to me , vCAC Provisions VM based on the Parameters provided by user now it could be vAPP`s VM or VM into vCenter,vCAC utilizes Machine Prefixes defined in admin Section which is why while customizing the VM it give it a new name out of prefixes pool.
Br,
MG