Paths crossing over

[alvgoro]

Paths sometimes cross over. It is usually when I move the balls fastly. I tried to solve the error cleaning the position vector when there is a change in the ball number. (When a ball goes in/out of the frame)

Here is an image during the error:

I guess, the problem has to be in positions vector. Or maybe when it draws paths...
It is interesting that the ball number is the same when the error occurs. Both balls has the same number (1 in that case)