So in my opinion the error is in the copy function of the line. If a line contains CoordNodes, than also the copy should contain CoordNodes. Can you point me to the code, where the lines gets duplicated?
Whenever a routable way gets split to limit the number of points or nodes it makes a new list of points so any changes to the points in the new list will not be visible in the original list.
Yes, its true that changes in the copy will not be visible in the original. But this is not my point. My point is: If the original line contains CoordNodes (instead of Nodes) then the copy should also contain CoordNodes. I think, this will complicate the split/copy functions in some ways, so maybe your solution is the easier way.
I have now looked into the code and must say, I don't understand why it works. Previous for each node was created a CoordNode. Now instead a flag is set. I see the difference: The flag is copied, the class obviously not. But I didn't find the place, where this copy occurs. Could you point my nose to the file and line number, where the line is duplicated? The only place I found is in the round coord filter class (line 55), where it is handled correctly. So why your patch works as expected and the original solution not?? I have another idea of solving this problem. Instead of do a new Coord or CoordNode call coord.copy(). The function could be overwritten in the CoordNode class to return a CoordNode object. (BTW. This should be done in the CoordPOI class too). So a copied line should contain afterwards the same types as the original.