Similar to the reported (and fixed) bug below, after picking Summon I in the Mage tree, you can take the Air Elemental summon skipping two skills in the tree.
"After picking Summon II in previous level, the next levelup I'm able to skip all the way to pretty far along the levelup tree. Probably a bug?
See image for details:
https://www.dropbox.com/s/sibazqm7u3dtyxw/levelupbug.JPG"
