You're right! I have frozen the diopter ring.
I suspect it's an accident. On other binoculars I have stiffened up the ring without freezing it up entirely.
I shan't try unpicking things for now. It's late at night, and I have to get up early tomorrow. But I shall have a go tomorrow or the next day. I daren't say definitely tomorrow because it's very hot here; I have a cycle ride tomorrow morning; and I may flake out afterwards.