When the player object has a wall to its right, event 9 enables 8 direction behavior and disables platform behavior. However, since the player object doesn't have a wall to its left, event 12's conditions are met, switching the behaviors back.
The fastest and simplest solution is to combine events 10 and 12. You can also combine events 9 and 11 with an OR statement so your events aren't redundant:
<img src="http://i.imgur.com/eadtvj1.png" border="0" />