this is something I have seen for years but never gotten around to report.
Sometimes when I edge modify a box (Shift-Ctrl select the edge and use Gumball to move up and down) I encounter situations where Rhino suddenly don’t want to select an edge any more.
See file and try to subselect the edge:
SelEdge bug.3dm (193.8 KB)
This happens when in RENDERED MODE only as far as I can see. Shaded works fine.
This happens in both V6 and V7.
To work around the issue I use the MoveEdge command. BUT this isn’t a good workaround because then I can’t also select other objects to move at the same time.
Please see if you can figure it out.
In the process please also add a wish for a SelEdge command that works just like subselecting but that filters out any other objects and that also works with “shift-drag-rectangle-selection” (in lack of a better word)