Hi Danny, thanks for reporting this - yup it appears that Merge has a problem fusing edges that cross right over the pole of a surface like a sphere.

I'll need to think about it a bit, but I think that the fix will probably be that Merge will have to skip those points and not try to merge them, because you can't really have a single continuous UV curve in that case. When you cross the pole you are going from one side of UV space to the opposite side very abruptly.

- Michael