Mine are doing the exact same and was just about to make a post about this.
Drove to Stuttgart and back yesterday (about a 500mile round trip) and when i started at 7am the lights came on, grand cos it was dark! but they stayed on the whole way. even tho it was 27 degrees and very sunny. Im not sure the speed thing is right tho, because same story today only driving around town, never went more then 70kph (about 45mph) and the lights we on all the time. was going to get it checked by the dealer...
Is there a sensor in the rear? i thought it was just the front, by the mirror?