Collider has the disappointing news that the Academy’s unpredictable music branch has disqualified this year’s scores from three top composers: Carter Burwell, Michael Brook and Clint Mansell.

[Mansell's] work for Darren Aronofsky’s Black Swan has been deemed ineligible for Oscar consideration due to its usage of music from Tchaikovsky’s Swan Lake…

According to Variety, Carter Burwell’s scores for True Grit and The Kids Are All Right (which he composed alongside Nathan Larson and Craig Wedren) and Michael Brook’s work on The Fighter have also been disqualified.

Confounding logic or any readily apparent consistent standards, the music branch says The King’s Speech score by Alexandre Desplat is good to go, despite the extensive presence of classical pieces on the soundtrack.

Also, didn't TSN use a bit of material from Ghosts I-IV?

The problem isn't on using classical pieces on a soundtrack as is the case of THE KING'S SPEECH. Desplat has composed original music for that film that isn't based on previously released material.

Mansell seems to have taken an existing piece of work and adapted and varied it into his score, and that hass been deemed ineligible since the Academy dropped the best adapted score category years ago due to a lack of candidates.

I wonder if something similar can happen to Zimmer's INCEPTION and his usage of 'Non, Je ne regrette rien', but I think the 'percentage' of use is minimal compared to the other composed material.