I had two thoughts on it. Either
a) Production, realizing teams would be bunched, enforced K/V's penalty on leg 5 so that it wouldn't be rendered moot, or
b) Production, wanting to move things along and noting that K/V were already in last, applied the penalty for them the first chance they could get, which would be the leg 5 pit stop, much like how time penalties on the US version for last place teams are added to their release time from the Pit Start.