I have one and have never been questioned. In my opinion it is no different than plugging a shotgun for migratory birds. It physically limits the magazine capacity, so it should be good to go.
By the way, okla. allows 7 in the magazine for .223. If you have an AK, or a upper in a bigger caliber, you can legally run 100 round drum mags.
More than likely a mag tuning issue using the 10 round. compare the feed lips on the good mag vs the 10 rounder to see if they are the same distance apart. Might just need to bend it slightly.
Does the 10 rounder make it nose dive into feed ramp, or does it jam with the round too high?