www. not working since 3.9 update

Current setup is a bunch of networks, going to the bare domain “foo.com” (in most cases). Up until the 3.9 update, anyone going to https://www.foo.com would still get the site at foo.com without having to do any additional redirects manually in .htaccess

Since 3.9 was installed, https://www.foo.com goes to the base network of the multisite install rather than the site associated with foo.com. This is happening on all networks in the multisite install.

This is, naturally, highly undesirable behaviour. I need to be able to put multiple domains into the network config if this was an intentional change. If not, please fix it.