I have a domain with Windows 7. Each user has a home directory assignment by a group policy. Their documents folder is redirected to this home folder. It appears that the home directory is automaticly setting itself as available offline. This is the behavior that I want, however I need to know why it is happening.

This behavior is by design. When you redirect an user profile folder to a network location it will be available offline automatically. This is because these profile folders are indexed by your Library. In Windows 7, network folders that are indexed in Library must be available offline. Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.