you're using a ceiling tile instead of a walltime, that is normal for them.
ceiling tiles have a special directional and automatic passability to allow simulating a two-level-dungeon in regular, one level map.
if you look carefully the tiles on A4 are paired - top and side of walls.
and you need to use them like that, with the top never directly connecting to the floor. Then you can only get to the top of the wall by an override like a ladder over the regular walltile below.
EDIT: and you are in the wrong forum, the screenshot is from MV but this forum is VX. Report it to a mod to have it moved.