Brake Pedal Goes to Floor After Brake Job... Bad Master Cylinder???

[jon6fountain]

Alright, I've read on here several others have had the same problem, but have not found a clear cut answer. I just finished changing all 4 rotors and pads on my 04 4.4i X5 with OE parts. I followed the DIY on here to the T. When I finished I started the engine and the brake pedal now slowly goes to the floor when I keep pressure on it. I can pump it up to a full pedal and it will be firm for a few seconds only to slower return to the floor. Everything was perfectly fine before the brake job was done. Could this be a bad brake master cylinder, and if so why has it shown its bad side only after the brake job??? Any help would be appreciated guys

Thanks,