When you run the DupEdge command and select the edge of a surface or polysurface it is possible to deselect that curve. It also seems possible to select the edges if the object is inside a block, but it’s not possible to deselect the edge of blocks while being in the command. Seems like a bug to me?
Hello - you’re right - & I don’t know how easy this will be to tune up - selection inside blocks has been a struggle I think. I’ll add this to the pile, thanks for pointing it out.