Well, I don't know how to correct this bug.
I've put a left-facing triangle and when I want to use it, there's two choice of bugs happening :
1. Go through the wall and fall in the void in the wall.
2. Go through the wall but this one acts like have been crushed so, I die.
When I hover my mouse over the tile it says :
"A left facing triangle that let Mario run up a wall. It requires tile 0x1EB underneath it to work properly".
Open the "Add Objects" window and go the "Direct Map16 Access (Lunar Magic)" and hover your mouse on a tile and the description should say you which tile it is. Search for tile 1EB and place it under the triangle.
Do you have any custom blocks in the wall that is causing you the problem?
Some custom blocks don't work properly with the triangle objects, for example, if you place a couple of No Mario blocks (the ones that sprites can go through only) on the wall to close off a small alcove with an enemy in it, you'll go through the No Mario blocks if you run up the wall.
I learned that one day in my hack, so lesson learned, be careful about using any custom blocks on a wall you can run up.
Have you tried using different tiles for the wall? There are a few objects that just won't work right with that object. Also, try making sure that the bottom part of the object (the ledge part) is on top of the ground tiles instead of behind.
Hmm... I remember something similar happening to me at one point. Try completely taking out the bit of ground under the triangle. Put the triangle (coupled with the "must be under triangle" ground where you want it to go. Test the level as is. If there's no problem, just use something to make it look right for the blocks 2 and more underneath the triangle, and don't have overlapping blocks under the triangle itself.
Also, if the wall is still messed up, try using Exgfx changed cement blocks for it to see if that fixes anything. I have a habit of not using the kind of blocks you're using for the wall, using a corner block where necessary and then normal walls, rather than the ground to top thing you're using. Either way if there's a problem after those changes are made I can't think that there's anything but a bad rom.