I have some preliminary response from eBay. They are not aware of any change, that made shipping or payment policy mandatory. My guess is that this behavior is an unintended site effect of some unrelated updated.
If you are running into this problem, please send me your eBay username (you can use the private message feature of this forum if like - just click on my account’s image). That’s usually the first thing eBay asks us for investigating such issues.