When does "Changes" tab gets displayed on Run Custom Build popup

I am using TeamCity 6.5.2 and I am system admin for this server.

I have observed that for some of my build configurations when I try to do custom build I can see "Changes" tab on Run Custom Build popup page while for some build this tab is not displayed.
I went through Teamcity documentation and found that "This section is available only if you have permissions to access VCS roots for the build configuration."
I have access to all the build configurations even then for some build configuration I can see changes tab while for others I don't see the tab. The documentation is not helpful in clarifying the cause. Can you please tell me when should I see changes tab and when not.




Regards
Ruby