Is the follower at an angle, IE, is the front of it higher than the back? And was the bolt on TOP of the cartridge rim or behind it?
I have only experieced this with the best rifle ever invented, the Ruger Mini-30 (ah hahahahahahaha...). This is usually a follower problem. Switch out the follower with another mag you have and see if it still works. If it does, then boom, compare the two followers and it should be some simple cutting to make the ProMag follower work.
How are the ProMag followers on the smoke mags designed? If they have a flate base on the end of the follower as opposed to rounded, then you could try cutting the two bumps out from the inside of the mag. This would make the follower push ALL the way up when feeding which could solve the problem, and if it doesn't, then you still get a BHO mag.