If you are editing the validations from the bindings Edit button on the main page, those settings aren't stored with the form definition. To edit the form definition so that the settings are save you have to drill into the preset and edit the field group and remove the validations from there. At that point you will be asked if you want to save your updates and they can be saved.
The form builder should not be used for form editing. Once a form has been built I'd strongly suggest editing the form manually within dreamweaver to add and remove fields. Using the builder will remove any edits you have made manually since the last application including updates to the bindings made immediately before application.