MU 'My Sites' dropdown only displaying Network Admin and Primary site links

I have 2 sites, using the same theme, in my MU network. The network is using sub-domains. All is working well but, at Super admin level, the My Sites dropdown is only showing links to Network Admin or my Primary site. Shouldn’t my second (sub-domain) site also show in this dropdown?

Sounds picky, but having to traverse Network Admin > Sites > Sub-domain Dashboard is annoying. I’m guessing I’ve configured something incorrectly?