Same url listed twice on Google

I noted same page listed twice on a serp of Google some months ago.
I thought it was a temporary Google's bug but this case has still been persisted.
The page is the home and the same link is listed twice (not the home page more an internal page).
I know same situation regards different serp for different keyword and different web sites.

The site, in those cases, is usually on the 8th or 10th position on the first serp's page and on the 11th and 13th on the second page.

Who does explain these strange results? :-)

other page/s rank too.. its not a strange situation.. totally normal.. ;-)

Not other pages but the same page in the same serp.

I think I thought the solution.

You have to create a sitemap in xml in a mather web site.
The web secondary site is excluded in that directory so mather web site and secondary web site are not associated.

Then you could create another sitemap.xml file and manually submit it through Google's Webmaster Central

On the other hand, I also think that when Google identify this technique you risk a ban