Tabbing should move focus between the three text areas. After having created a new transition one usually wants to use the "Edit Transition" dialog to enter both Guard, Sync and Update. After having entered a guard one expects that pressing tab will give focus to the Sync text area. This is not the case.
The same might be said about the enter key. But I do not agree that one expects tab to move to the next field and enter to be equivalent to pressing ok: This is the case for single line fields, but not for multiline text areas (see Swing user interface guidelines). Here tab and enter should insert a tab character or a line break. The behaviour you request can be achieved with ctrl-tab and ctrl-enter. Again, see the Swing user interface guidelines.
Should I mark this bug INVALID or what should we do about it?
In 3.5 the meaning of TAB and control TAB has been reversed.