BuddyPress - can't add user on my subsite (multisite), any idea?

Hi,

I've got a subsite (multisite network) with BuddyPress and bbPress, this one:
http://template-rencontre.creersonsite.net/
But when I add users they don't show up inside the member list.
I guess I'm doing something wrong but I can't figure out what it is.
Any idea?

Also, I saw that there are more than 1000 pending members. I guess most are spammers, but many seem leggit. Is this possible that they are some members of another subsite inside my network? Very weird...

Thanks!