Thank you for that KB! We have ESXi 5.1U1 deployed, but VMTools is 9217 (9.0.1, build 913578), which if I'm correct is from patch ESXi510-201212402-BG. We have not deployed the tools from 5.1U1: VMTools 9221 (9.0.5, build 1065307.)
I implemented the workaround with success, as we are not yet prepared to roll out VMTools 9221.
Would still be great to know though if there's a way to specify a VM clone spec without quiescing? Thanks again!