According permissionDefinitions.xml, contributors have full permission on what they have created - via the permissions assigned to the owner. While the web client works in this way, cifs do not.
As contributor you can create a content and you are the owner of it. Now if you enter cifs and try to drag&drop that file over __CheckInOut.exe, Alfresco will show you the following message: "Not a valid Alfresco CIFS folder".
It's quite strange, but if you have the collaborator role (or both contributor and editor), even cifs works properly.
It seems that user has not write permissions even if he is the owner. If you add the following permission to the contributor definition then it works:
<includePermissionGroup type="sys:base" permissionGroup="Write"/>
Is it a bug?
BR,
Alessandro