Hi PaQ, thanks for posting that - the edge preview not showing is related to the inverted normals.

In the mesh preview, if the object is closed (every edge joined to another edge), mesh edges are not shown for backfacing polygons to help clean up the display and reduce edges that might bleed through thin areas.

However, in this case the orientation of the object is inverted, also inverting that backface detection.

The bug is in some earlier process that did not calculate the orientation of the surfaces towards the outside of the object correctly... Unfortuantely it will be difficult at this point to figure out which operation didn't do that properly.

Doing a Separate and then re- Join like Petr mentions does do a proper job of determining the "outside", that's why it fixes this up.

Please let me know if you run across this again or if you notice any pattern that you notice the inversion happening after a particular operation.

- Michael