Ports dependencies strangeness.

I've been seeing this pretty regularly with several
different ports:

 * Start with a fresh system with no packages.
 * Try to install some port with a lot of dependencies
   (using -DBATCH so it won't keep stopping and
    asking for configuration options)
 * At some point it stops with a missing dependency

But:

1. Scrolling back through the console output, it's clear
    that the dependency in question has in fact just
    been built and installed.

2. Package tools show the required dependency is installed.

3. Restarting the original build does not rebuild the
    dependency but does notice that it's installed and
    goes right through.

Somehow, it appears that port dependencies are
getting built and installed properly but not always
being noticed by the main build.

Tim