In easy
Search engine consider www.1tb.net and 1tb.net both as different domains will www.1tb.net is being considered as a subdomain of 1tb.net thats why both have different PR
This problem is supoosedly being fixed by google.Until then the best thing you can do for your domains is to do a 301 redirect from the non-www domain to the one with www. Or viceversa,whichever you prefer.
That way you avoid this "site-splitting" issue.