Sigil Games and Microsoft are parting ways on the development and distribution of Vanguard: Saga of Heroes, and Sigil will buy back the rights to the game. 

From the press release on sigilgames.com:

Sigil Games Online and Sony Online Entertainment announced that Sigil is working with Microsoft Game Studios on an arrangement to acquire the rights to its highly anticipated massively multiplayer online (MMO) game, Vanguard: Saga of Heroes. These efforts have resulted in a tentative agreement for Vanguard to be co-published by both Sigil Games Online and SOE. All three companies will be showing the game at the upcoming Electronic Entertainment Expo (E3) as they work closely together for a successful transition. Vanguard: Saga of Heroes is scheduled to launch this winter. ...

“As the development process is ongoing and constantly shifting, it became clear that MGS and Sigil had varying visions and direction for the title’s development,” said Brad McQuaid, CEO of Sigil Games Online.  “In the best interest of Vanguard, it was decided that we would buy back the publishing rights from Microsoft.” ...

”This decision was made mutually by Sigil and Microsoft, in the best interest of the long-term goals for the title,” said Phil Spencer, General Manager at Microsoft Game Studios.  “As a key Windows development partner, we will continue to work with Sigil to ensure Vanguard’s ongoing success.”

There's also a Q&A with Sigil CEO Brad McQuaid on VanguardSOE.com.

....We remain good friends with the folks at Microsoft and look forward to creating a AAA MMOG for them, even though it will be a 3rd party Windows game now, and not a first party. We had some differences, but the biggest catalyst here was that we found the opportunity to buy the publishing rights back, which is good for Sigil no matter what else did or didn't happen.

Like I have been saying, this gives us even more (perhaps even unprecedented with a game this far along and this big) control, a chance to be a co-publisher, and to all around have more influence on how Vanguard turns out. Even were things perfect (and things are never perfect), it was an opportunity that couldn't be passed up on.