After editing a query and hitting the back button, there are several codemirror instances on the page, but only one is expected to be there.
please give a step-by-step scenario: is this about inline editing a query? and do we click on Go after editing the query?
in the simplest case:
* open main pma page
* click server_sql tab
* click back button in your browser
* click forward button in your browser
This bug was fixed in repository and will be part of a future release; thanks for reporting.