Interesting that you find this bug not effecting your races especialy for an endurance series.
After the pit stop the lap times are more then 2 sec slower. Higher wear of rear tyres(before pit stop front tyres are wearing more). On the straights top speed is 5 kmh lower.
In our first endurance race we had, our fastest driver was leading the race for about 8 sec in front of me. Race lenght was 33 laps. He pitted at lap 14 while I pitted on lap 22. I came out 12 sec infront of him. I gained 19 sec by pitting 8 laps later, on worn tyres!
As you know it's impossible to gain time on worn tyres in racing. At least that was the case in GT5.
So I can't see how it's the same for everyone in this case. It's far from it imo.
So we decided in our GTF forum and Pure series in this forum there is no way we can do endurance races untill PD gets around these issues.
Hopefully PD will sort this out in the next update.