For anyone interested in adding their name to the pile and wanting to avoid the 10 days of time I spent trying to get this through to Tier 3 support so they can finally acknowledge it's 'unexpected behavior' - use INV-83565 as that's the investigation number I was given. So frustrating - but the more that pile on the better as this is an exhausting bug. Made worse by the fact you can't permanently delete a vendor - only making inactive. We've got dozens upon dozens of unwanted vendors now.