After importing a GR1 track, both of the edge flags appear to be on the same side.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3006942292

After moving the left waypoint flag the right flag is not on it's line.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3006943002

Moving the right flag makes the red edge lines go goofy.
Note that the arrow is reversed.
https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=3006943451

Moving the flags to the correct side makes the direction arrow reverse then snap back to the correct direction.
I think the flags are reversed and their position is determined by the left edge line.