A light spring could be your problem, but I'm still betting on the locking bolts on the new barrel. They might need a little polishing to allow them to trip the interlock properly. The combination of the lighter springs and the new locking bolts could be causing the problem. By replacing the factory springs, the sear is able to make a better "purchase" on the engagement surfaces, but I'll bet there is still a chance of an accidental discharge with this new barrel.
My bet is the locking bolts on th new barrel. With G2 Contenders, which are built very similar to the Encores), the problem comes up when older barrels will not trip the interlock, but the G2 usually will not cock at all. We usually polish the lock bolts a bit and every thing is fine.
Call MGM and let them know the problem, and suggest that the bolts may not be engaging fully. See what they say.