Am I mistaken or did I see a Model 50 Reising SMG mixed in with the A3s.

In one scene I saw a Thompson M1928 and (what I think was) a Reising M50 SMG. I understand that the marines on Guadalcanal initially used the Reising but were both weapons issued concurrently in the same unit?

What's the story on the Reising SMGs? Were they intended to replace the Thompsons and did the M3 "Grease Gun" subsequently replace them?