Hahaha, wow that's dodgy!! Hopefully there's a patch soon. Thank you for your suggestions - you were on the right track. Someone responded to my HP forum post with a suggestion to import the vcenter self-signed cert into the trusted root cert store, and after restarting vSphere client, it started working at last:
I got to the cert by browsing to https://myvcenter:3504/ as you suggested.
thanks!
Ray