cloak of arachnida

I noticed that my character wearing the cloak of arachnida couldn't walk up trees when I was in a combat in the forest.  I wouldn't have thought much of this, but we were fighting against spiders hiding at the tops of trees!  So, I haven't gotten to try using this item on dungeon walls, but I figured there should be a way to use this to walk up vertical surfaces besides walls where applicable, right?

I noticed some similar issues with fly -- even using shift+scroll wheel it's really hard to position some abilities and movement on the vertical axis. Maybe there's some additional way this could be handled?