[Brexen]

Can you confirm these things for me?;

User Permissions (Usergroup Manager)

for Regular Members;
Can edit own posts: Yes/No? (Set this to yes personally)

For Moderators:
Can edit own posts Yes (Make sure this is yes)

Do you have Moderators assigned to the appropriate forums?

If so, all should be fine. The only problem I can foresee is that you have it set up so regular members can't edit their own posts, and that moderators can. But because the moderator isn't assigned a forum yet, he adopts the permissions of regular members, so cannot edit his own posts.