I think this is a holdout from earlier game build rules:
Previously you could only put 3 PPCs in the Hunchback 4P's shoulder box, and loading a 4th PPC wound up placing the weapon in the chest cavity below the weapons box. Apparently there is not enough room to put the model for 4, 5, or 6 PPCs in the shoulder box or something.
Well, now is the only time in the game's history where you can physically fit 5 PPCs' worth of slots on the Hunchback's Right Torso. The game does not know how to handle this because the artists never assigned a 5th PPC location for the dynamic modeling, so it defaults to putting a laser mount in the shoulder to represent the fifth PPC.
FYI
Edited by Prosperity Park, 28 June 2017 - 07:18 PM.