Oh yeah… I got a little distracted... erm... QAing my work. Yeah, that's the ticket. Thanks for the reminder, 709. I wasn't just playing Nintendo for the last half hour.
Surprise! The solder joints were the cause of the failure. So, if you buy one and it conks out, give this solution a try. All I did was touch each of the five USB connections (pictured below surrounded by the white print) with the tip of the iron until the little residual solder on the tip started to flow.