Just a note to people - this is not the way to post a bug. As this one has been explained to me outside the forums, I will take a moment to add some details.
When sliding along a track which has a repeat symbol, you currently have to be on *top* of the repeat symbol at the time of intersect, rather than anywhere in the larger "safe" circle. This is incorrect behaviour, as you should be able to stay anywhere inside the safe circle and keep your slider active.
Will be fixed in next build.