Probably has more to do with the gun itself than the ammo. I use to bumpfire a lot, and never had a problem with steel ammo, laquer or not. I have a feeling that some of the guns out there are .223 chambered, not 5.56, which some people will tell you are the same, but the .223 is slightly tighter, which makes for more malfunctions than any difference in ammo. My AR will shoot brass or lacquered steel just fine. My take is there are shooters out there with the .223 barrels who are having fits with their guns, and blaming it on the ammo.
I have heard the same thing. My AR is chambered to 5.56 but I buy 2.23 cause it's easier to come by and cheaper!