I didn't add to Herald as I wasn't sure whether it's specific to these forms or if there are other forms which have these components and the same problem.

oops~

Yeah, these are "common" controls, but I think they only get used in Herald?

Herald has some very unusual code to preserve control values when you swap the selectors. Generally, the issue is:

• when you change the <select /> controls in the first two columns, that may change the type of control in the third column (e.g., from a typeahead to a text field or to no control);
• if the old and new controls are both of the same type, we try to transfer the value between them.

I'd guess something is off with the "copy the value" code.