As stiv32 says, compare the Filename field. Select both tracks, and look at Filename in the Tag Action Window. It will say [Varies] if the Filename fields are different, and will show a single value when they are the exactly the same.
Also, add an expression column in the file list (right click the file list column headers, Add Expression Column... and enter the expression:
FileKey()
and OK your way out. The file keys should not be the same, and if the Filename fields are exactly the same, you're probably experiencing a bug that several of us have reported.