Here's a follow up. I took my bike back to the LBS yesterday and they replaced the chain at no charge. They even refunded me the installation charge for the first chain, the one that broke. I asked what they found with the old chain (which I retrieved on Sunday) and they said they should not have installed a 9 speed chain on an 8 speed drivetrain. I'm no expert but from what I've read that shouldn't matter. It's moot anyway. The new chain is an SRAM PC850 8 speed chain.