I think other people must have noticed that quite a while ago, but i never saw an actual post dealing with it, so I'll post it in here.
The server and client seem to have different opinions on how long the tail of a cycle is. If I hit the ending of my trail on the fortress server my cycle gets stopped dead and the rubber goes up. But after a fraction of a second the cycle jumps to where it would be if there was no trail at all. I guess it's a correction by the server...
This is sometimes annoying if you have a high ping and defend on fortress... you get no real indication where the heck you really are and have to guess when you follow your own zigzag trail as close as possible (you don't want anyone to get in