"Nico
Drivers will race 2 Laps in Qualifying (Outlap and Fastlap). They start with 10L of fuel and the ideal temperature for their tyre compound, which is different from tyre compound to tyre compound.
There is no usage of DRS or KERS and therefore laptimes will definetly be slower than race laptimes.
By 10L i assume you mean 10 liters and not 10 laps. So when they are on hot laps, they will be down to around 6 - 6.5 liters depending on the track. It's comparable to the example that i gave. My driver was on lap 27 of 28 lap race, started the lap with 10.8 liters, it's actually heavier than qualifying hot lap.
But important point is this:
Driver was on full back off push level, and didn't use KERS/DRS in this lap. He was on wet tyres on a wet track. It's hard to believe this can be faster than a dry qualifying lap. Even with track rubbering as the race progresses, i don't think this is the case in reality.
This doesn't affect the game play as such, because the race lap times seem consistent enough across races and account for dry and wet weather, so the bug is not about wet race lap times in comparison to dry race lap times. The bug is about qualifying laps being slower in general, which result these kind of anamolies.