Losing the signature when updating resource

If I update resource without clicking in the "attach" button I will lose the previous data(lost signature).

Also the "saveOnChanges()" won't help unless you sign again.

I notice when updating the resource the (textarea for the signature) will give you a default value, that is a transparent background. example below. And that is the data that get saved in the DB.

What I'm looking for here is just when saving the resource keep the same signature with out clinking in the attach button.

data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAYwAAACUCAYAAACAyx4IAAAA+klEQVR4nO3BMQEAAADCoPVPbQdvoAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAeA2UgQABdXK3UQAAAABJRU5ErkJggg==