This number 9223372036854775807 at the end of wordpress permalinks

I just noticed in my google webmaster tools that there are 404 errors and they are pointing from my permalinks whcih have this number in the end : 9223372036854775807.
for example this url : http://www.designzzz.com/beautiful-pictures-nature/ is show as this http://www.designzzz.com/beautiful-pictures-nature/9223372036854775807/ and works fine..
i got worried that there might be some hacking or other issue in my site and google it. i found that many urls from different wordpress sites are indexed with this same number in the end. so i am curious what is this about.
Google QUery