Okay, so the Big Link hitbox makes Link react to anything that he encounters in a 16x16 square of his input source, instead of the 8x16 square of the little hitbox.
The problem is, when he's walking sideways from a fully-walkable combo to a half-walkable combo in the sidescroller screen, he doesn't stop for the half-walkable one. He just keeps on going.
This is kind of hard to explain, so I'll attempt a drawing.
~ = Walkable
# = Unwalkable
_ = Space Holder (There so you can see where one combo ends and another begins)
Link will be moving from left to right in this example.
~~~~~~~~__~~~~~~~~__#########
~~~~~~~~__~~~~~~~~__#########
~~~~~~~~__~~~~~~~~__#########
~~~~~~~~__~~~~~~~~__#########
~~~~~~~~__#########__#########
~~~~~~~~__#########__#########
~~~~~~~~__#########__#########
~~~~~~~~__#########__#########
Link starts on the left combo. As he's walking, the walkable flags should stop him in the middle combo. But he passes right through it as if it's a normal walkable tile. Link stops as normal upon reaching the completely unwalkable combo.
Doing a short hop with Roc's feather corrects this little wall-walk. Also, I've only tried it in the gravity-enabled screens. It would seem that the Big Link Hitbox will treat combos that have the top walkable as completely walkable, but I believe it only does this for side-scrolling rooms.
Could someone else test this to verify if it is actually a bug? I did have a FFC on this particular screen that disables items when facing a particular direction, but it seems unrelated (So I don't think that's the problem).