Ah... a nice little tactic, if it hadn't been because the legionary himself would have buddies to his sides, actively engaging the spearmen. These spearmen would have trouble to change to a new target. A target that might very well pull out of range as soon as the shield is lost (and thus not kill the falxman, or perhaps just enough time to do that).
Also the legionary could do the opposite, and actually pull the falxman closer. It depends on who does what first. If that happened the spearmen, even if they were able to strike, would have one of their own blocking their venue of attack. Meanwhile the legionary would make short work of the defenseless falxman.
Generally warriors did not spend a lot of time on liberating their own equipment from troubles. Such as the Helvetii that didn't take the time to remove the pilumheads from their shields (which can as easily be said of the Germans and Gauls in the same campaign).
Do not forget that getting your weapon caught in something, was not good. Quite a few shields are speculated to be designed to actually snag the enemy weapon so that the attacker would be open to a strike. I don't know if this is a fact, but it has certainly been speculated on a lot, and does seem to have a basis.
Now I ask, where do you get the spearman/falxman combo, as anyting other than the flaxmen stiffening the more general spearmen, while the spearmen provided the falxmen with some defensive strength. But would hardly be much different from anywhere else, and could as easily be accidental. As a lot of cultures had leading individuals in the society lead less well armed persons into combat. Hence giving them a sort of swordman/spearman look to outsiders.