Yeppers. Probably happened to a lot more than will admit it. (or it will). You have to make it an effort to constantly check that the jag is screwed on tight to the rod. It has a tendancy to back off and that's when it breaks.
I had one break off inside my traditional a couple months ago. Actually it came loose and the treads stripped out as I tried to pull it back out. (it was stuck in the breach somehow).
I had to take it out to the woods and take out the nipple and pour in some FFFFg and shoot it out.
At least with an in line you can get to it from one end or the other.