Probably everyone knows, multisite allows to create a site when a user types non-existent alias. For example, if the main network domain is domain-1.com and in the network we haven't such site as sub-1.domain-1.com, but we'll type it manually, the system will start registration procedure for site sub-1 in domain "domain-1.com".
Unfortunately, in "networks" environment such thing is possible only for the domain, which is definad as DOMAIN_CURRENT_SITE in wp-config. If, for example, in our networks we have a second network, which has a domain, for example domain-2.org, and we'll try to type non-existent url, such as sub-1.domain-2.org, then the system won't start registration procedure on "domain-2.org" for subdomain "sub-1", but it will try to set up a site like "sub-1domain-2org" on domain "domain-1.com". So, the result site will have such URL: "sub-1domain-2org.domain-1.com"!
I tried to remove DOMAIN_CURRENT_SITE from wp-config, and it helps for registration, but then any site won't work with www at the beginning.
Please think about this issue in the future release.