[Sasha94]

I'm not sure the glow plugs have much to do with this; on the 2 136ps 2.0D's I had before the D5 I never saw the glow plug light, they don't do much on modern diesels until below freezing. On my D5, if it's cold outside the procedure is much the same as the OP, touch the button and wait. Sometimes there's a split second wait after releasing the button but no matter what, it always spins the starter motor over enough to start the car then stops by itself. I wonder if an experiment could be conducted to see how the start button on the OP's car is working? I mean as in remove fuel to the engine and press the button. Will the engine keep turning over or will the OP have perfect control of the SM? My point being that it would seem some programming is involved here to spin the starter until the engine fires, I wonder if this is not clutch related and has something to do with the wiring to the starter motor.

It's a very bad idea to try this with fuel still flowing into the injectors but I know if you press the button on my D5 with the engine running the starter motor won't spin; it knows it's already running. If your car isn't engaging this computer control to spin the starter for say 10 seconds or until the engine starts whichever comes first and you have total control of the starter then there is the possibility that you could continue to press the button once the engine is running and still spin the starter. This would pinpoint the fault but it's not a good idea to do, hence I wonder about testing in a scenario you know won't start the engine.

Re cruise, having an auto, I can't help there, I can only confirm that the brake pedal on my car disengages the cruise as soon as it is pressed.