The Preselection is based on the Main Table key value that is set on the Second Step of the MRT behaiovr.
On the insert page this is set to use a session variable that is created by the Insert Record behavior.
It uses that Main table key value to query the relational table and return the IDs of the options selected for that record.
on the update page, it is a URL variable that is used.
to prevent the insert page from preselecting the previous records selections, you can clear the session being used by the MRT behavior. I normally set the MRT behavior to detail page. So on the detail page unset the session, for example, in the MRT Tutorial the session used is named WADA_Insert_items.
on the detail page, click the plus button in the server behaviors panel, select webAssist -> Cookies -> Clear Session Values.
Set the trigger to before page load. and from the list of sessions, select the WADA_Insert_items session.
the preselection cant be used on validation failure since it relies on the data being stored in the database.
