N step WF: impossible to set WF roles

6.0 r22127

I have set some groups for each role of my N-step WF, but when I try to go trough the different steps of the validation process with my different users, I can't even do the first notification. I have so edited again my roles, and no one has been set. I have so redifined it, and reedited: every thing has been lost again, even using apply button, then ok button.