Why don the markings stay accurately on the ground?
There are some limitations to what information is available to addons. Things affecting AVR the most are lack of any information about the Z-coordinates of units (the elevation), and lack of precise camera position. Everything is drawn as if it was on level floor at the same height as your feet. When you move up stairs, start flying, jump or move vertically in any other way you’ll see the markings move with you. Similar thing happens when the camera bumps into a wall, ceiling, floor or some other obstacle. AVR only gets information where the camera should be and draws all markings according to that. If the camera bumbs into any obstacles then it will automatically move into a different position. AVR can’t detect this and so it draws markings in wrong positions. You shouldn’t expect for these things to get fixed over time. The information needed to fix them simply isn’t available for addons. Naturally Blizzard could make this information available in a future patch but that seems unlike