try running it with -d5 and a logfile specified in the config file. That will throw out errors that will explain why it can’t index those songs.
The permissions do indeed seem to be right, so I’m not sure what it might be.
Check the config file and make sure the mp3_dir is right… no spaces after /share/hdd/data/public/mp3, for example.
That’s about all I could think of, but the -d5 will show you more info.