IM, I assume the repro ejectors are made the same as the original ones Parker Bros used, this system is quite complex and has a sear-trigger arrangement. The hammer should stay in the cocked position unless the barrel fired and the gun opened. It should also stay cocked when you remove the forend. Chances are one of the delicate sears is damaged or not engaging or it could be dirt or an obstruction is keeping it from working correctly. Probably best to see a competent gunsmith who is familiar with these ejectors.
Jim
