I hope this helps:
1) It isn't just facebook messaging issue.
2) It's not related to force update.
I went on stock 7720. Updated to 7740. Then 8107. Then 8112. Then 8773.
All normal Zune updates. No forcing.
I don't have facebook integrated. I don't use it. However I tried WLM. I am constantly offline to everyone on the friends list and so are they to me. However, when I log into laptop version, I see everyone, they see me, we can talk.
This persists on 8112 and 8773. Nothing to do with integrating facebook or not AND force updating or taking the official update.
HTC Titan Euro version is my phone. So probably unrelated to OEM. Most likely something that messed up messaging hub lies in 8112 and 8773.