Hi Steve, yup that is definitely the sweeper thinking that it got close enough and not adding in enough refinement in that area.

This part tends to be a difficult thing to balance because if the sweeper checks for accuracy in too many places it will cause it to take a really long time to complete in more complex cases. But if it doesn't check enough it can let things like this by.

I've added this to my chunk of sweep-related work to see if I can fix it up.

- Michael