strange permalink behaviour with categories

Hi,
accidently I noticed that I can put any word after a category and there won’t be any problem with the link.

For example the correct link:
http://ma.tt/category/review

but I could also write
http://ma.tt/category/coconut/review/
or even
http://ma.tt/category/coconut/cocktail/review/

and it won’t result in a broken link.

Technically it would be duplicate content, wouldn’t it?
Any ideas how to solve this?