This is a dilemma that all Windows programmers face. Should the Tab or Enter key be used as screen control characters (skip to next field, or save the record), or are they to be used as text formatting characters (tab character or new line). If you change to one type, those that depend on the other will complain.
Some programmers will use a multi key press (Crtl-Enter or Shift-Enter) to indicate the other type of use. Unfortunately it seems that Memento does not do this.
As Memento staff do not usually read this forum, an email to Memento Support can be sent suggesting this change.