Originally Posted by kerry edwards

That makes sense. I didn't look closely enough upon disassembly but it seems like the best hypothesis yet. It took some prying with a screwdriver to get that spring out so it was probably right against the backing plates.
It seems like a design flaw.
It would also explain why I thought for a while that perhaps the rear brakes were the only ones working. I had a sense that the car was not 'diving' enough during hard braking, making me suspect the front brakes were the ones not doing their job. The spring limiting the amount that the pads could squeeze would account for that sensation.