It is more common than many realize. Mostly with older guns. I have a 1974 rifle that has dropped the firing pin on an empty chamber a few times with no pull of the trigger. Mine has only done it for 1 day about 10-12 years ago. Never before or since. It did it 3-4 times over about a 30 minute period and stopped. As a result I've done lot of research, long before any programs on TV. You will get some replies claiming it is all a plot by anti gunners to hurt Remington. These guys have their tinfoil hats on a little too tight.
A little history.
Remington engineers discovered the problem in 1946 and advised management to redesign the trigger. Because the new rifles were already behind schedule on production and a redesign would have meant recalling rifles and adding 5 cents to the cost of the guns management decided not to make the change.
The problem is a device called a trigger connector. With every other trigger design the trigger is connected directly to the sear. Pre 2007 Remingtons have a connector between the 2. It is a small piece of sheetmetal that slides between the 2. It is very easy for a tiny bit of debris to get inside the connector, or for the connector to malfunction. When this happen the sear releases the firing pin, but the safety prevents the gun from firing. When the safety is moved to the "fire" position the gun fires with no trigger pull. The problem is hard to duplicate or predict because what ever is messing with the connector will often fall out and the problem goes away.
It is just as likely to happen to a brand new gun as one that is 40 years old and never done it before. It might happen once or twice in a lifetime, or never.
Remington was hit with a flurry of lawsuits in the 1970's. About 2 dozen people died and well over 100 have been injuried. As a result Remington redesigned the safety in 1982 making it possible to unload the chamber while the gun was still in the safe position. This did not address the real problem, but it did drastically reduce the possibility of the inident happening. After many more lawsuits Remington finally did away with the trigger connector on guns made after October 2006.
Remingtons take is that only guns that have had the triggers adjusted improperly or are dirty will do this. This is partly true, but what they don't tell you is that a single spec of unburned powder that falls into the trigger connector will disable the gun while a handful of mud in any other design will not cause this. I have no doubt that in some cases improperly modified triggers do cause poblems, but there are thousands of cases of new, unmodfied guns doing this. Mine has never been modified.
Here is a Consumer Reports article from 1968 where a new rifle they tested did this repeatedly. Bottom left column of page 2
Remington claims they have never been able to duplicate the problem, but here is an internal memo from 1980 where 152 rifles were returned to Remington with complaints. They were able to duplicate the problem with 52.