COM Interop and the Execution Context

Question

Hi All,
 I have a thread impersonating a user ABC. Within the thread create an instance of a COM object and i notice that an operation fails due to permissions to a folder. Upon further investigation, i discovered that the user context that the COM method is running was Network Services and not ABC.
I have looked online, but cannot find good documentation on COM identities and impersonation. Why does the COM object not inherit the parent threads context?
Thanks,
Preetham