Package deinstall woes since new portupgrade arrived

[Tobias]

Howdy freebsd-questions - almost every day I run a "portupgrade --batch
-rav" over my installed packages on my "FreeBSD 8.1-RELEASE #0" system. Two
days ago I noticed that portupgrade itself was updated and that subsequent
packages had troubles updating.

Here's a sample for a "portupgrade --batch -rav" run:
...
===>  Building for p5-Set-IntSpan-1.15
cp IntSpan.pm blib/lib/Set/IntSpan.pm
Manifying blib/man3/Set::IntSpan.3
--->  Build of math/p5-Set-IntSpan ended at: Tue, 09 Nov 2010 23:38:41 -0700
(consumed 00:00:01)
--->  Updating dependency info
--->  Uninstallation of p5-Set-IntSpan-1.14 started at: Tue, 09 Nov 2010
23:38:45 -0700
--->  Fixing up dependencies before creating a package
--->  Backing up the old version
--->  Uninstalling the old version
--->  Deinstalling 'p5-Set-IntSpan-1.14'
** Listing the failed packages (-:ignored / *:skipped / !:failed)
        ! p5-Set-IntSpan-1.14   (undefined method `nil' for "":String)
--->  Uninstallation of p5-Set-IntSpan-1.14 ended at: Tue, 09 Nov 2010
23:38:56 -0700 (consumed 00:00:11)
--->  Upgrade of math/p5-Set-IntSpan ended at: Tue, 09 Nov 2010 23:38:56
-0700 (consumed 00:00:16)
...

It appears as if the deinstall fails for some (at least to me) unknown
reason. p5-Set-IntSpan was not updated and we end up with lots of stale
dependencies that need to be fixed via "pkgdb -F". If I manually do a "make
deinstall reinstall" in the port-directory then the deinstall does not have
any issues.

Does anybody know where I should be looking for a solution to the
"(undefined method `nil' for "":String)" problem?

Thanks - Tobias