[@jkovis Participant 15 years, 1 month ago]

You are using outdated versions of both WPMU and BuddyPress. I urge you to upgrade.

I also had the same problem last night on a fresh svn check out of https://svn.buddypress.org/branches/1.1/

I just updated to newly released 1.1.3 and now the correct activation link is sent.