I think you're wrong with this one seeker.

I think that only files that have the same filename AND filesize
are grouped. So i.e. you can still find 'BLABLA.avi' and 'BLABLA [DivX].avi' both having te same size.

And if, like in this case, you know that both files are in fact the same file...it will be a handy option if you can say to the program that these files are in fact the same, and that it can use both of these 'source-groups' to download the file.