From This steam group

"As of the Christmas update of 2013 there was a patch to prevent conflicting items to be worn together. This was a glitch that harmed no one and only gave players more freedom to enjoy the game yet Valve found it necassary to rip it away from us. Here is a place you can disscus, show pictures of old clipped loadouts, and plan ways to get equip regions removed so we can freely wear our items."