Say I have a simple WP multisite install (if there is such a thing ;-) consisting of 2 domains.
DomainA.com is my master domain, and DomainB.com the other domain. I'm using Domain Mapper.
I'm logged into wp-admin as a network admin user on DomainB.com.
I click Howdy Admin -> Network Admin and get redirected to wp-login on DomainA.com ... and have to enter my un/pw again.
I could've sworn that was working before but now it isn't and I can't recall if I've broken something or if it is due to cookies not working across domains...