Some of the USE flags in the sys-libs/pam ebuild are not documented at the above-mentioned URL. Specifically, I couldn't find documentation for the pam_chroot, pam_console, pam_timestamp, or pwdb flags.
That's because they are not global. They are perfectly fine documented in use.local.desc
Well frankly said those flags don't even exist in sys-libs/pam, what's this bug about?!