I recently got hold of a Lapdock, and was busy trying to make up my own cable adapter to turn it's Micro Male connector into a Mini Female one to make it more generic so that I can use it for anything and not just splice together a Pi specific cable (where anything might be the Pi, or a headless PC, or a PS3 etc...).
Having done this (using all 4 wires, and not omitting the red power wire because it may be needed for other uses) I hooked up my Pi from it's regular full size USB slot(s) to the lapdock with a perfectly normal USB Male to USB Mini Male into my adapter cable:
Normal Full size USB to Mini Male cable >
My Mini Female to Micro Female Adapter cable >
I was surprised to see this power up and boot the Pi successfully into a GUI. I have an original board (Hardware Revision 002), and it's one of the first batches without the polyfuse removal, and neither have I modded it to bypass them. Admittedly, none of the USB attached devices that are part of the lapdock (KB/Trackpad/USB Hub) actually worked (Which seems odd as they draw power from the lapdock internal battery and not the Pi) until I subsequently additionally powered the Pi through it's proper power-in connecter (powered from the lapdock USB hub of course...)
It's not causing me any problems, and I intend to power it normally anyway, I would just like to understand how this can possibly work with my Pi in the first place? Can anyone explain it?