The point I am trying to make is that regardless of what eBay says in its seller guides, the system is (at present)  AUTOMATICALLY imposing a "defect" for any partial or full refund put through Paypal.

I have done that often ( in the last 6 months).. partial refund through paypal (voluntarily refunded part of postage costs when they are more than actual costs) and have no 'defects' when looking at the new seller standards thing on the dashboard.