stale dependencies in pkgdb

[Andrew]

Hello,

I am trying to use a combination of portaudit and portupgrade to
automatically maintain installed packages on my system, but portupgrade
often hangs on stale dependencies. I've run "pkgdb -F" as portupgrade
suggests, deleting stale dependencies, but they seem to keep
reappearing. I guess I'm a little unclear about what a stale dependency
consists of and how to fix it. Pointers to relevant documentation and/or
explanations would be greatly appreciated!

Thanks,
Andrew