When you use tab to switch between cars in a paused replay, the flag-messages are not updated.
Example:
http://www.abload.de/image.php?img=blueflagn38.jpg
Notice how the 1st car seems to have a blue flag, which can't be.

I think that its normal. That also doesnt seem to be an big issue.

Yep - its because LFS only updates things like that when the replay is actually running.

"LFS only updates things like that when the replay is actually running"
thats what i wrote

Of course its no big deal, but if it was "normal" why are laptimes, minimap, tyres etc. displayed correct and only the flags are wrong?

Because an lfs replay file is like a list of events that happen, which are then triggered in-game. When you switch between cars, the map and times stay as they should be, because there is still that trigger there. However, flags are not updated between cars whilst the replay is paused.