I am trying to add a hard drive to a VM. I selected the check box disable storage DRS for this machine so that I could specify the individual datastore in a cluster instead of 'keep with vm'. And, I selected thin provision. I click next or ok and it refuses saying "This operation would violate a virtual machine affinity/anti-affinity rule." I got it to work by letting it create the drive in the same datastore as the rest of the virtual machine and then used migration to move that hard drive. But, what the heck is this about!? What does any of this have to do with affinity rules? And no, there are no affinity rules that involve this virtual machine.
My guess is that this is a bug.
vCenter 6.5 (accessing with Firefox. Was using Chrome, but then I renewed the certificates and that blew up Chrome for this app.), ESXi 5.5.