Just to update, I did get a response from PP, and it was as expected.
They still didn't tell me why they've made this decision (although I believe it's because I sold two items on ebay, just testing the waters).
It was just a standard form email, and they repeated their usual carp about "commitment to security" and "valued customer feedback" (to be expected).

So, you complain to PP and you get no answers, just a repeat explanation of the initial problem. No solutions. Not even a recognition that there is a problem.
So, I think it fair to warn people that if they start a site using PP, and then decide to explore ebay as a sales option, DON'T DO IT unless you truly believe your sales will increase and you are happy to accept PayPal's dictatorship over your finances!
PP state this as one of the reasons for withholding funds, and as I have zero customer complaints, this has to be the reason.