I wouldn't say that it "just broke." At first, the seatbelt in the car got caught between the case and my belt. As I got out of the car, it pulled the clip back to the point where it locked into the stand position. Hearing the noise, I stopped and checked it out.
The second time, I was just sliding into the car, and the box pressed against the side of the car seat as I slid into the car. That's when the belt clip twisted and broke the plastic hinge loop.
The unit comes in six assembled pieces: 1) the case back, 2) the case front with screen protector, 3) the belt clip holder, 4) the swivel unit on the back of the belt clip with the bottom part of the clip, 5) the top part of the clip that you squeeze, and 6) a metal "V" piece that provides the spring tension. The bottom part of the clip has two loops that hold two posts molded onto the sides of the squeeze part of the clip. The posts are fitted into the loops on the bottom section. It's one of these loops that broke.
I have heard stories of thieves stealing these phones off of people's belts by snapping the unit this way. I'll have to be more aware of the position of this unit on my belt in the future.
Steve