Point on path moves beyond path

Both of these points are constrained to their respective paths in the exact same way. Constraint is set to “Simple constraints”, and I’ve added one “to path”.

This screenshot is at the end of the animation. At the beginning both points are on the endpoints on the left side of the paths. Now at the end you can see the point on the upper path has traveled beyond the end. What is causing this?

Can you please post/send me the model so that we can have a look at what’s going on?

I’d love to, but I screwed up and saved over the file after screwing around for it a bit and the problem disappeared. If I can replicate it again, I will upload a model.