I just added a pull request to add the "^" plus a few other extra checks adding/removing symlinks that tidies up the sequence: install squid, install squidGuard, remove squidGuard, remove squid. It resolves all the package install/remove interactions that I can see, particularly those caused by "squid" being a substring of "squidGuard" and "squidGuard" being a mixed-case package name. Hopefully the changes to /etc/inc/pkg-utils.inc will also fixup generic issues for these cases for other packages.
I have tested with the new 22 March 2012 2G nanobsd FreeBSD 8.3-RC2 snapshot.