Just my opinion and I don't want you to take this the wrong way but for you to ask what could cause such a malfunction means you probably don't have the skill or working knowledge of the 1911 to make the repair. My suggestion is very simple, take the firearm to a qualified gunsmith familiar with the 1911 and let him diagnose the problem and fix it. Anything short of that is potentially opening yourself up to serious legal trouble. Hammer follow can occur with out of spec parts, wear, or can be caused by a misguided attempt at a trigger job. Just my opinion but let a gunsmith take care of this one if you aren't one yourself.
Tom