I would expect that any quantity of tweens started from the same "frame" would be always syncronized. But since SimpleActuator set the "startTime" var with:
every time a new tween is instantiated, each instance gets a slightly different time and thus get desynchronized from the others.
As a fix suggestion, maybe instead of lazily listening to Event.ENTER_FRAME, listen to it before any tweens are instantiated and keep a single value from Lib.getTimer() as startTime.