This isn't so much a bug, just something that got missed getting implemented, but a small thing that I've noticed, when you engage the pit speed limiter before you enter the pits, that small flashing light on the rear of for example GT3 car (and others that have them), doesn't appear to flash, like I'm pretty sure it does in rear life.
That's the rain light, it's not being used during pit stops in GT3 cars. The headlights and rear lights might flash instead, but that's different for each car.