Password reset sent from top level blog (id:1) instead of originating blog

We have WPMU set up with a few domains on it (configured as separate domains rather than subdirectories).

A strange thing has been noticed.

When a user of blog_id 6 goes through the “forgot password” workflow, the reset email is sent from the first site to be inducted into the WPMU build. Blog_id 1.

So the message is headed, styled, and has a login link included that are basically from a completely different web site, from the user perspective.

Is this familiar to anyone?

Thanks in advance!