Hi Marc,
there are still elements with the same id, for example in my test of the
sakila database, there are two elements with id footnote_1_1.
The source of the problem is the following. When db_structure.php is
executed, it calls PMA_showHint() which keeps track of the number of
instances for each message in a global array.
However, when you call tbl_change.php via AJAX, the global variables are
reset and this execution is not aware of the previously recorded instances.