inconsistent dependency information

[Scott Webster]

I have three ports installed that claim they have no dependencies:

[~@skadi]$ port dependents p5-xml-sax-expat
p5-xml-sax-expat has no dependents.
[~@skadi]$ port dependents xorg-libpthread-stubs
xorg-libpthread-stubs has no dependents.
[~@skadi]$ port dependents xorg-xineramaproto
xorg-xineramaproto has no dependents.

But other ports claim that these are in fact library dependencies:

[~@skadi]$ port deps p5-xml-simple
Library Dependencies: perl5, p5-xml-namespacesupport, p5-xml-sax,
                      p5-xml-sax-expat
[~@skadi]$ port deps xorg-libXp
Build Dependencies:   pkgconfig, xorg-util-macros, autoconf, automake, libtool
Library Dependencies: xorg-libXext, xorg-printproto, xorg-libpthread-stubs
[~@skadi]$ port deps xorg-libXinerama
Build Dependencies:   pkgconfig
Library Dependencies: xorg-libXext, xorg-xineramaproto

All these ports are installed.  Is this a bug?  If so, in what?  Base?

Thanks,

Scott