I get the same thing whenever I sign into the MS Facebook app for the first time after a ROM flash. If you find out the answer, please post it here.
Maybe something in the registry, I'll have a look at that...
So, I noticed that at:
[HKCU\Software\Microsoft\Facebook]
"UserActionPublished" is 0 before you log in and changes to 1 after you log in. Perhaps changing that to 1 before hand would work... I'll give it a go after my ROM finishes flashing and report back.
OK, so I flashed my ROM and before I signed into the MS Facebook app I went to my registry at the afore mention place and changed that "UserActionPublished" value data to "1". Then I went in and signed into Facebook. Then I went online on my PC and the last activity it shows it me installing Facebook for Windows Phone 40 minutes ago, which was when I signed into Facebook earlier, about the time I first posted this post.
So, it seems that this regedit will do the trick. Facebook is still not showing me as having installed it this time.
Edit: Here's a cab with those regedits already in it for those of you not familiar with editing the registry. Soft reset after you install the cab. You could also just toss it in your UC or Sashimi directories and have it autorun as part of your set up, just a thought.
@ Any random people who don't read the entire thread and install this cab...
Obviously this .cab or manually changing the registry are only effective if you haven't signed into MS Facebook at all since having flashed your last ROM. If you've already signed in to MS Facebook then this cab and registry edit won't do anything as the damage is already done.