User custom fields dropdown field getting scrambled

I’ve got a UCF dropdown with 31 options, in a carefully curated order. After saving, the bottommost 4 went to the top, and all the rest shuffle down. The editing was in Chrome on a Win 10 machine.

This occurred again after I patched it up (again in Chrome).

Patching it up in IE11 after this worked and now it is sorted.

Yes, I know that 31 options seems excessive, but I have a good use-case!!