The NTFS permission model doesn't map one-to-one with the traditional Unix-style filesystem permissions. In fact, it barely maps at all even under simple, narrow permissions structures on the Windows side.
I've seen various scenarios where the permissions reported on the Unix side were nonsensicle, or indicated permissions that weren't being enforced (for example, files where the permissions show as not world readable, but being able to be read by the world nonetheless).
Have a look at what security configs are on the directory you're mounting up from the Windows side; it might point you towards the problem. But by and large I wouldn't plan on observing parity between NTFS and traditional Unix-style filesystem permissions.