Bard Song and You

The description says you go DOWN from 5 AC to 4 at level class level 23. This was not my experience, so I thought the description to be wrong. I mean, why would my song get -worse- as I level up? And at first it didn't, but now at class level 26, I see that my AC given by song -did- go down to 4. I think this must just be an error somewhere more than likely. And yes, my perform rank is high enough, at least according to the description. I'm not really complaining so much cause it's still good, but it's not like it SHOULD be. I've had 5 AC from song since level 16 bard, 10 levels later I certainly shouldn't get -less- stats from singing. Perhaps 16-22ish should still be 4 AC and then you hit 5?

Noticed a simaler thing with courtisan bow on my ranger at level 20 ranger it gave me +4 on my bow now with 23 ranger its +3 odd. Maybe something to do with not being a pure class in epic levels .