Martin,
Thank you for your response. I ran the subject completely (cross and long) in v6.0 and the white matter intensity distribution in the long brain looks similar to the one run with the mixed versions (v5.1 cross and v6.0 long). Since the surfaces also look fine, I understand that this is not an issue.
Thank you again, Jaiashre.
freesurfer@nmr.mgh.harvard.edu