There is nothing wrong with the carbine length gas system, the problem comes from when you actually put a carbine length barrel on said gas system instead of the 16" one that is typically used. The problem is the distance from the muzzle to the gas hole in the barrel, the shorter the distance the less gas time there is less gass time less gas, open the gas hole to compensate too much and now you have ammo sensativity and extractions issues.

This is why the gas system on the Bushmaster dissapator was moved back from being part of the front sight.