Hi Michael,

I've been using the merge command lately to clean up edges after some boolean and trim operations, it works great! until this situation;
I made a sphere, boolean difference in half with a line in the center, parallel to the sphere seam.
Then shelled the half sphere and merged the inside edge and the outside edge.

When merging the inside edge the inside surface converges towards one of the poles.

When merging the outside edge the outside surface disappears, but the half sphere is still a solid, if we fillet that outside edge the outside surface re-appears.

This doesn't happen when the line used for the boolean is perpendicular to the sphere seam.



Cheers