Hi,
Which version did you install? and what kind of version of OSC are you using? Sounds a version conflict to me. I have the contrib installed and its working fine. The only problem i had was with attributes that has 0,- as value (like colour). When i dont use a prefix he adds up the initianal value in the sub-total list. I couldnt fix it properly but fixed it use the + prefix. So know he adds up the zero which is no problem in the end.