dpkg-scanpackages isn't designed to take in some of the user defined fields Cydia repos use. Saurik points out in his How to Host a Cydia Package post how to easily fix this.
This is rather easy: simply add "Name", "Author", "Homepage", and "Icon" to the end of the array "fieldpri".
Not sure which one the mac specifically uses, but you can find the script files for dpkg-scanpackages in these locations assuming they might be in the same spot:
Otherwise do a little search from the root directory with:
sudo find . -name "*scanpackages*"