You might notice that defacto was posting in reply to the peculiar FD problem on airbus aircraft. And yes, in that regard the boeing is much more simple. Doesn't matter at all if one FD is on, both, or none, in both manual and automatic flight.
The ALT CAP thing is usually not a problem with proper training, its demonstrated once during the initial typerating and then each pilot uses one of several methods that prevents it. However, it is an autoflight issue and not a FD one.