Site with double url for the same products

[DaSco]

The url of detail product on this site are dupiclated?

For the same product there are two different structure:

www. sitename.com/category1/category2/name_of_products.html#.code1

http://www.probolt-italy.com/index.php/cycles-4-wheels/kart-kits/titanium-bolt-kit-rear-axle-gokart-crg-125cc-09.html#.T8PmAMX9VsV


www. sitename.com/name_of_products.html#.code2
(when I click on "PART NO:")

http://www.probolt-italy.com/index.php/titanium-bolt-kit-rear-axle-gokart-crg-125cc-09.html#.T8Pmq8X9VsU


Why there are two url?