Contacts listed as "mobile" contacts (ie. with mobile numbers set up) have a little cell phone icon beside their name by default when they sign out of the official Windows version of Live messenger. On the Mac version, I don't believe there is such an icon, but the contact information remains the same across platforms.
In version 1.0.1, when a contact meeting these qualifications signs out, they actually remain "available" or "online", but instead their little symbol beside their name (in the Adium contact list) will change to the mobile version. If you try to message them, obviously, they won't receive the message (unless they have forwarding set up so it goes to their actual mobile device).
I have reverted back to 1.0, and everything is fine as it used to be.
Please make use this information if you can.
