In the dark when you've switched off and locked up they will flicker for about 5 mins, as the bulb sensor is still active.
I replaced mine last year along with the third brake light bulbs [501 x5] but it looked a bit daft flickering away at night, so i put the stock one's back in.
I have how ever but in cool white halogen ones which look miles better with out the flicker issue.
PS, with the led's i never had an issue with bulb fail warnings
LUIGI