Can't Change Virtual Disk Formats When Targeting a Datastore Cluster

As I work more and more with vSphere 5 I am finding a few anomalies. One of them appears to be a bug where you cannot switch a VM’s disk format during a storage vMotion, when you target a datastore cluster. To be more precise, it looks like you should be able to, but it doesn’t end up happening.

The workaround is to disable Storage DRS for that VM, target a datastore directly, then edit the Storage DRS settings afterwards to re-enable DRS for that VM.

This is what it looks like when I try. I select “thin provision” from the virtual disk format, choose a datastore cluster (in this case it’s my “Tier 2” cluster), and click next:

 

Looking at the VM settings to confirm that it’s thin… hey, wait a second:

 

That’s not what it’s supposed to be. But, when I move it back and try it again with Storage DRS disabled (and be careful, it likes to flip the format back to “same format as source” when you check the “disable” box):

 

Then it works fine:

 

If you edit the datastore cluster properties (Datastores and Datastore Clusters -> Select the cluster -> Edit Datastore Cluster -> Virtual Machine Settings) you can re-enable Storage DRS for that VM:

 

I’d suggest putting it back to “Default (Fully Automated).”

VMware Support has opened a bug on this, and my SR is 12133278201 if anybody needs it.