When proper and backward/upside down beams cross
3-way prism
Before
After
4-way prism
Before
After
See these images?
In the images about the 3-way magic prism, the sword beam that moves right faces left after the original sword beam is fired downward at the 3-way prism.
In the images about the 4-way magic prism, after the original sword beam is fired downward at the 4-way prism, the beam that moves right faces left, and at the same time, the sword beam that moves up faces down.
In the top image, you'll see areas where beams are crossing each other. On the upper side, each pair of crossed beams has one appearing correctly, and the other flipped upside down. On the right side, each pair of crossed beams has one appearing properly, and the other flipped backwards.
AND HERE'S A MAJOR UPDATE TO MY CURRENT TEST QUEST! (I ADDED MANY NEW SCREENS, INCLUDING THE ONE SHOWN IN THIS THREAD!) http://www.freewebs.com/masterpikachu/ZC%20Content/Incomplete%20Quests/LOZ%2DGeneration4.qst
MINOR UPDATE: MADE A FEW FIXES TO MY OVERWORLD MAPS! (This minor update to my test quest has nothing to do with the bug)