google do not have any filters in place. and they allow you to create multiple shortlinks for the same URL.
and the shortlinks you get are different from the shortlinks i would get.
i understand that some users might want to keep an eye on stats for different short links for the same link. for example, i might use one on Facebook but the other on Twitter and compare their performance. but still!
basically, they are wasting a lot of four digit shortlinks which is just sad...