The pamd file installed by ppp at the moment is not good for Gentoo. It should use the same setup I suggested for freeradius in bug #210882.
bug 210882 does not exist
The bug you are referring to is bug 210822. Fixed in ppp-2.4.4-r14 (I've kept the KEYWORDS from previous revision).
(In reply to comment #1) > bug 210882 does not exist > In the mean time however it does exist :-)