Why are disks inflated on Storage vMotion?

[vitaprimo]

Since 6.7-ish I have noticed that pseudo-randomly (almost all the time) when Storage vMotion is performed, thin provisioned disks are inflated even after the process itself presents the option to change storage policy to be used on the target datastore, even if it's clearly stated early on in the docs that networked storage (in this case) defaults to thin provisioned disks. I'm now on 7.2 or 7u2--IDK, there was an update just days ago but it still is happening and I've cannot find the reason why. I checked storage policies, even tried finding some pointer in vROps but it's all normal.

I have noticed that there's better chances for this to happen if I go through the "proper steps" of performing Storage vMotion, e.g; list the list of VMs in the bigger area of vCenter, select from the dropdown or contextual menus to migrate the VMs than if I just group them by power state, select them in a series and drop 'em into another datastore in the tree at the left side. The same questions appears; if I want to change storage policies, if I want to keep DRS, the works, except it wouldn't take as long to move them because it's not unnecessarily wearing out storage.

Another workaround I found it to be ZFS storage, I think it stems from its ability to compress on-the-fly, it's performing calculations so it catches when vSphere is just zeroing out stuff. I really don't know the reason but I'm happy to lie to myself with that. Still don't explains why vSphere is blatantly inflating disks though. It has already finished inflating all VMs. I avoid over-provisioning so I'm good but that could easily get out of control if when snapshots considered: this other time I moved a powered off VM, it was maybe 60GB written that resulted in nearly a terabyte (about 3/4TB) with only 3 snapshots; 256GB inflated snapshot disks. the thread must be still around. It did not happen again thankfully. Storage DRS I think it's safe, but since all of my VMs are already inflated I can't really know for sure. Standard vMotion since it doesn't really move anything permanent, is fine too.

Anyone has figured this out? I've reinstalled vCenter twice since v6.7, more if you count the updates. Since it keeps happening I think maybe it's widespread bug or misconfig overlooked in between updates. Thanks!