I really could not see the purpose of this one. At the end of level 3 there are actually 2 river stones on top of the wall:
So why don’t these show up on a C64? Well, they actually do show up, but with colour overridden with grey. Have a better look below:
I really like to have the choice not to override colours when using Integrator 2012 as that shows me details that would otherwise be completely invisible, as proven above.
Update! Check what happens without these two river stones:
Can you see now why these were needed? I bet you can!