Word file ownership changes after edit/save.

Question

This may be a server issue more than Office, but I've come across some articles relating to this problem in Samba, and thought it might be similar.
I'm the Network Admin for a school district.  We have a file server that is setup with a file and folder structure that allows students and teachers to access and share documents.  One teacher came to me with a problem.  Students are able
to create and save Word documents to an assignment folder.  The teacher then goes into the document, makes changes and enters notes, then saves the document back to the folder, overwriting the original.  The problem is that once she has done so,
the student can no longer access the document.
After investigation and testing, I've found that ownership of the file is changing from the student to the teacher.  This is a problem based on the way that the ACL is set on the folder.  The students' access is based in the creator/owner attribute. 
The fact that the ownership is changing once the teacher opens and edits the document is causing the student to no longer have access to the file.
My question is, is there a setting or other change that can be made to Office so that ownership is not transferred to the teacher?  Giving each user explicit rights to each file and/or folder isn't really an option when I have 3000 students to
deal with.  Again, this may be a server side issue, but I've not seen this problem with other programs. 

Answer 1

I'm picking this up because I have the exact same problem. 
Students are given Write access to a folder (So they can save their work)
Teachers are given Modify acccess to a folder (so they can add comments, etc)
CREATOR/OWNER is given Read/Execute so students could read teacher comments, but not make changes to the document once it has been saved.
When I test it with my admin account, it works great.  I can update the document and the student can open it to see my comments, but not change the document anymore without saving to a different location.
When I test it with a teacher account, the document changes ownership as soon as the teacher saves.  Once the ownership changes, the student no longer has permissions through CREATOR/OWNER and they can't open the document to see the comments anymore.
I can't see why this works when my account makes the changes, but not when a teacher account does.  We are doing the exact same things in Word.
Here is an example of the permsions as they exist on a sample document.  In the example, my admin account (which works fine) gets it's permissions through BUILTIN\Administrators:
PS H:\> $acl = get-acl "L:\TeacherShare\S2 3(A) Study Hall - Half Year\Submissions\StudentWork.docx
PS H:\> $acl.access
FileSystemRights : ReadAndExecute, Synchronize
AccessControlType : Allow
IdentityReference : SCHOOL\StudentAccount
IsInherited : True
InheritanceFlags : None
PropagationFlags : None
FileSystemRights : Modify, Synchronize
AccessControlType : Allow
IdentityReference : LPS\TeacherAccount
IsInherited : True
InheritanceFlags : None
PropagationFlags : None
FileSystemRights : ReadAndExecute, Synchronize
AccessControlType : Allow
IdentityReference : LPS\School Principals
IsInherited : True
InheritanceFlags : None
PropagationFlags : None
FileSystemRights : ReadAndExecute, Synchronize
AccessControlType : Allow
IdentityReference : LPS\School Document Administrators
IsInherited : True
InheritanceFlags : None
PropagationFlags : None
FileSystemRights : FullControl
AccessControlType : Allow
IdentityReference : BUILTIN\Administrators
IsInherited : True
InheritanceFlags : None
PropagationFlags : None