Problem with save on samba shares

Did:

I opened an existing Qt project file (.pro) from a project stored on my Samba-shared home drive. I tried to edit one of the source files contained in that project.

Expected to see:

I expected to be able to save my changes.

Got instead:

I got a warning strip at the top of the editor panel:
"Warning: You are changing a read-only file." with a "Make writable" button.
I cannot make it writable and cannot save the changes without renaming the file.

More details:

In our networked environment, our homes are stored on Unix file servers. They are shared via Samba to our Windows XP pro workstations.

When I open an existing project file from a software project on my home, the files are properly listed in the Projects panel.

The files are not read only and they are owned by me. The Unix permissions are 644 and ANY OTHER editor on my computer can modify the files. If I change the Unix permissions on the files to 666, the read-only warning goes away. If I use 664 mode, the read-only warning comes back.