According to pkg_add -v, pkg-plist executes the following commands:
ln -sf bin/toast /usr/local/bin/tcat
ln -sf bin/toast /usr/local/bin/untoast
which create these incorrect links:
/usr/local/bin/tcat -> bin/toast
/usr/local/bin/untoast -> bin/toast
Replacing %F with %f in pkg-plist removes the extra bin/.