Default User role not setting on MU BP site

When signing up, new users are not being assigned a default user role on the main site.
With BBPress installed, they are given a Participant role, but that's a forum role only.

I noticed if the account is manually activated then the user role is assigned as default.
User role Editor is used to create the default roles.

[Vaughan: I set Writer & Participant roles in User role editor default roles settings]

This worked perfectly fine for the 3 accounts I created when activated via the Manage Signups page in Dashboard > Users > manage signups.

But didn't seem to work if using the activation link in the email. The users are created for the network, however, they do not have a role on main-site or are even listed on the main-site.

Not sure what could be causing this.