Comment 4 for bug 712499

Confirmed that some combinations of cursor positioning can trigger this bug.

The problem is that the new ID subfield was getting inserted into the wrong location in the DOM for the XUL display - but not in the MARCXML. A workaround is to switch to the flat-text editor, then switch back to the classic MARC editor; the XUL elements will be recreated based on the MARCXML and the Validate button will work as expected.