non-standard-dir-perm lintian warning for 2755

[Adam Lewenberg <adamhl@stanford.edu>]

I am getting this warning when running lintian (version 2.4.3):

non-standard-dir-perm var/cache/project/ 2775 != 0755

N:
N:    The directory has a mode different from 0755, and it's not one of the
N:    known exceptions.
N:
N:    Refer to Debian Policy Manual section 10.9 (Permissions and 
owners) for
N:    details.
N:
N:    Severity: normal, Certainty: possible
N:

However, when I look at the referenced section of the Debian Policy 
Manual it says (in part): "Directories should be mode 755 or (for 
group-writability) mode 2775."

So why is lintian complaining?