TestComplete 9 fails to identify if a script unit in a project integrated with SVN is locked by other user

I am using TestComplete 9 for functional testing and since more than one person is working on this project we maintain our Testcomplete project files in svn. i am facing a problem in following scenario. 1. User1 checked out a script unit or name mapping and working on this on his PC. 2. At the same time when user1 holds the lock, User2 is trying to check out the same scriptunit or name mapping. 3. test complete allows user2 also to check out the scriptunit though it is already checked out by user1. 4. Since user2 was allowed to checked the script units, he does the modifications and tried to check in and it displays error message. In this state, if user2 tries to do undo check out, get latest version it fails to do. i am confused that why user2 was allowed to check out the file which was already checked out by user1? And why user 2 was not able to revert the changes when it was not allowed to check in? somebody please help.