No, it's not a common problem. But I reckon every rider has been caught out by a snapping cable on some occasion. If the break was really inside an unbroken portion of housing I'd suspect that the cable had been kinked prior/during installation, and then slowly working itself apart ever since. Breaks at point where it's a more obvious local load, as in/out of housings, anchor points etc are far more common - or rather less uncommon.