cruvon,
The Brake Pad sensors on the E90's wear down as you use your brakes.
You MUST replace the sensor when you replace the pads and only reset the service indicator when you replace the sensor. If you reset the service indicator when the sensors are below a certain wear level you will fire off the fault you are seeing.
I Made the same mistake with my car but I simulated the sensor wear level using a Resistor and then performed the reset so the car thought it had new pad sensors. I then Put the old sensor back in and the usage went back to where it was. Id say you probably have a faulty front sensor or was damaged during install and your rear has now been reset so your going to need a new sensor or simulate a new sensor.
BMW's diagnostic machine or INPA will tell you exactly what the wear percentage is which would tell you what the front sensor is doing.
Hope thats of some help
