Something must have changed recently. Characters that have no stroke data are getting stroke allocation prompts on the mnemonic dialogue, but clicking on the numbers doesn’t do anything. They don’t seem to register the clicks at all.
I still see this very occasionally, most recently with 龖, but I have no idea how to duplicate it. It’s harmless, but could potentially be confusing to other users, so let’s keep an eye on it.
It happened for the mnemonic you have there currently? I did a straight copy/paste of that one, but the prompt did not appear for me. Must be a transient thing.