[reported by @web010]

If a page contains multiple forms, a changed form cannot be submitted. All forms are checked and when the last form in the checker was not the submitted one, the checker gives a 'false' on 'was_submitted' and a true on 'changed input', which results in the returnmessage.

I don't, but it might be a good idea? Especially seeing as it's only one file.

If a page contains multiple forms, a changed form cannot be submitted. All forms are checked and when the last form in the checker was not the submitted one, the checker gives a 'false' on 'was_submitted' and a true on 'changed input', which results in the returnmessage.

Second problem is the checking of an editor which might be part of the form. I solved this by adding the options with "editor:check_editor". check_editor (default=false) is a callback function in a custom script. In the function dontJustLeaveMe I made the following change:
$(window).on('beforeunload', function() {
if ( ! was_submitted && options.editor){
dirty_editor = options.editor();
}
if ( ! was_submitted && (dirty_editor || options.serializeForm($form) != initialState) ){
return options.errorMessage;
}
});