I apologize in advance if this topic has been covered before.
My understanding of Combat feats is that you can only use one per round. Looking at Deft Shield, I see that if I make a shield bash and hit, I get to keep my AC bonus. Very nice. A few levels later, I look at Shield Slam and see that I can make a free bull rush when I hit. Very nice, except...have I now lost my AC bonus from my shield? A few levels later, I'm now a "Shield Master", and get to do lots of wonderful things with my shield (and I have my shield AC bonus back) but now I can't have my free bull rush anymore. What happened to being a "master" with my shield?
Would it be so unbalancing to say that I get to keep my AC bonus with Deft Shield (on a successful hit only, can't get greedy), add the bull rush ability on top of that with Shield Slam, and then take away the penalty to hit and add the magic bonuses with Shield Master? In other words, can't combat feats of the same tree be cumulative?