Engine doesn't shut off after replacing fuel return hose

[rino]

Never had shut off problems since buying my 240D eight months ago...
It always shut off promptly upon turning the key.

Two days ago I replaced the fuel return hose segments, which had been
leaking for some time. Right after doing that, the engine just doesn't shut
off any longer after removing the key, it just keep running indefinitely.
Even pushing down the shut off lever inside the engine compartment just
slows down the engine idle, but it doesn't shut it off.
To shut it off I've resorted to putting it in first gear, pushing on the brake
pedal and slowly lifting the clutch pedal until eventually the engine dies off.

What is going on?