Hey,
I'm facing the exact same problems on my Alfresco 3.4.8 with Windows 7 and CIFS.
Most of the users leave the files open through the cifs all day long, and at the end of the day, they want "save" their work BUT they "often" get a "save as".
Now, I'm thinking about a lost cifs connection. If they never touch the cifs mapping, the cifs is still there but certainly unreachable. They get a red windows 7 cross flag on their drive. They should get a green one.
Did you get any ideas about your problem because it seems to be very similar.
Please let me know if something new comes up.