So - I popped one of these in the fridge last night after a week of bottle conditioning. Despite, obviously, being premature, it has started to carb nicely and really tastes darn good for just 1 week. Not sure what the issue was, but it doesn't seem to be having a negative impact on the final product at all. It's got a nice rich color and all the mocha-goodness I was hoping for.
Can't wait to taste it again in a few weeks!