I normally run the command
# pkg_version -Iv | grep \<
before running 'portupgrade -a', to see what's going to happen. This time I got the following output:
diablo-jdk-freebsd6.i386.1.5.0.07.00 < needs updating (index has 1.5.0.07.00)
It seems that the tool is confused by the i386 in the package name.