[SOLVED] NTFS Operation Not Supported (45)

[PLEASE JUMP HERE IF YOU WANT TO GO STRAIGHT TO THE SOLUTION]

I have been struggling with a few permissions related problems and would really appreciate some help:

This is my setup:
- User mode permissions
- A share called "lifepractice"
- Two users (one called "karen" and another called "mshields")
- Both users belong to the group "users"

I want both karen and mshields to both have rw access to files and rwx access to directories. The users are accessing the files via windows using CIFS. I don't want any other users to have any access to files or directories.

In the FrontView CIFS tab I have
- Default Access: Disabled
- Write-enabled users: karen,mshields

In the "Advanced CIFS Permission" tab I have set
- Automatically set permissions on new files and folders: true
- For both file and folders/directories I have set "Group rights:" to "Read/write" and "Everyone rights:" to disabled.
- Enable oplocks for this share: true.

In "Advanced Options" I have set:
- Share folder owner: lifepractice
- Share folder group: users
- Share folder owner rights: Read/write [actually this is greyed out]
- Share folder group rights: Read/write
- Share folder everyone rights: Disabled
- Grant rename and delete privileges to non-owner of files : True

The problems arise when one user creates a file and then another user edits that file and re-saves it. For example:
1) mshields creates the file test.doc

 ls -l test.doc
-rw-rw----    1 mshields users       24064 Sep  3 16:44 test.doc

getfacl test.doc
# file: test.doc
# owner: mshields
# group: users
user::rw-
group::rw-
other::---

So far so good.

2) Next karen opens test.doc, changes it and saves

 ls -l test.doc
-rw-rwx---    1 karen    users       24064 Sep  3 16:48 test.doc

getfacl test.doc
# file: test.doc
# owner: karen
# group: users
user::rw-
user:mshields:rw-
group::rw-
mask::rwx
other::---

This is where things seem to go wrong.
Problem 1 - The owner of test.doc has changed from mshields to karen. Why does this happen? I thought that in Linux, when files are edited by a different user, the file will still retain the original user as the owner.
Problem 2 - Somehow the file has gained group execute permissions. How can I stop this happening?
Problem 3 - The ACLs for the file have an additional "user:mshields:rw-" entry and an additional "mask::rwx" entry that weren't present before the second edit of the file.

Problem 3 causes rsync to report errors when backing up to an NTFS USB drive (see the backup-related problem http://www.readynas.com/forum/viewtopic.php?f=31&t=44972&p=255310 that this causes).

I guess I can live with problems 1-3 if there's no alternative, but I really would like to avoid the rsync backup failures that are a consequence of Problem 3.

Thanks for any help.