Not safe

I bought two of these car seats for my twins. I bought them because the National Highway safety administration gave them a really good overall rating. I've had them for about 14 months and just yesterday while pushing down on the overhead bar to latch it, the overhead bar broke off. The plastic on both sides of the bar snapped right off the base. It was cold out, but I don't think they rate car seats based on planting zones - maybe they should on this one. Anyhow, I've dealt with car seats by all sorts of manufacturers for the past 8 years now with 4 kids and I've never had one break on me. If it breaks with the pressure that I imposed on it, how well does it stand up to a car accident? I am going back to the other manufacturers...