In the spirit of giving back I've spent a good bit of time tinkering with AI pathing. The AI pathing algorithm assumes that every bit of terrain space is walkable UNLESS that terrain is blocked by an object that has walk through and walk on set to false (there may be exceptions to this but this seems at least generally true). You can use the AI Grid Panel -> Paint Movement tool to manually paint any terrain that you don't want characters to walk on; which is probably what Larian has done with their maps and what makes regenerating the AI pathing give a different result when you copy.
Overall painting pathing seems *very* easy in the tool so I don't know that the copy issue really needs a fix. It would be a nice QOL improvement, but definitely not a 'must have'.
