I was attempting to build a Skirnir Magus, but some of the Skirnir archetypes abilities were not added to the magus and thus locked out certain feats or required you to take extra feats to compensate.
Skirnir archetype states that the magus is proficient with shields but they don't get the shield proficiency feat. It also says that they get their full magus level as fighter levels when concerning shield feats. I didn't notice that happening either.
Completed: At revision: 24550
This deals with the Bug reported:
1) No Proficiency with Shields, including Tower
2) Not qualifying for Fighter Shield based feats (Thus only one I found was Great Shield Focus)