This is a bug or at least a limitation.
For example, look at this very serious task of UV mapping toilet seat
Named selection degenerates after modifying the mesh - UV Texture unwrapping unwelds some mesh edges and because of that Named Selection made before unwrapping no longer works.
I can see how welding/unwelding could trip up a saved edge selection. But ideally any saved faces/polygons selections should always try to survive any welding, unwrapping, even exploding, correct?
Hello - unwrapping, if you specify seams, changes the number of vertices and ‘edges’ (which do not really exist as they do on breps) so any indexing to the previous mesh is completely useless.
Hi Pascal, yes, that’s the way its done today, because Rhino’s logic is very rudimentary. For example, even if specifying seams changes the number of edges, because they get duplicated, those edges are sharing same exact positions, and they have been doubled up by a command (a trackable event). So I think there’s room here for Rhino to keep track of this and know that an old loop is now two coincident loops.
Modo for example can even keep UV unwrapping information, even if you add/removes polys from a model. How do they do that? they designed their system to be paying attention to neighboring geometry and to what commands are the ones changing what.
It can be done, and like all good work, it’s just more work. I think this, like any other form of non-destructive editing is also important work.