Seriously, some guy went to jail for having a gun malfunction and go full auto.... though there seems to be a debate as to whther he knew the problem existed, or had a full auto group in the gun ... or whatever.
You don't want a gun that triple fires.
This needs to be fixed.
Besides it could ruin your day if it goes off out of battery, as suggested .... 
That guy was quite a famous case across lots of the Internet, and he hailed from my native WI as well.
You're thinking of David Olofson.
The .gov was pretty heavy-handed in that case, and what would have been fair is for local LEO's to say "get that damn thing fixed" and come back and show us it's fixed, and we'll call it even. Instead they did the usual tech branch testing and monkeyed with the gun until it did fire a few bursts. It would fire bursts with soft-primered commercial ammo, but not hard-primer military/NATO spec ammo.
OTOH, he's not exactly a squeaky clean individual. He left the military under a cloud of suspicion for missing equipment, had lots of other anti-gov associations, internet postings, and was also under investigation for subverting military computer systems to allow outside access to third parties. And there is some evidence he did play with the Olympic Arms AR, and lend it with a "wink and a nod" of what it actually would do.
All in all, it's the kind of case where he probably should have gotten off on technicalities to protect the rest of us who may have functioning guns and are innocent. OTOH, he was a pretty dirty individual who had been doing LOTS of things to bring the attention of the .gov on him, and a normal individual with a malfunctioning weapon would probably not be in much, if any legal peril.
Despite all the hand-wringing on the pro-RKBA blogs, Newsmax, WND, and various gun-boards, when you look at the totality of Mr. Olofson's situation, it's not quite so alarming.
