Global Site Search Pagination issue with UTF8 characters

Hello to everyone!

I have a problem with Global Site Search and Pagination.

When I search for something and I have more than one pages, in the results, after the first page nothing appears in the second, third etc.

I have a multisite and I configure the global site search for searching products from Marketpress.

Let's do now a recreation of the problem to see exactly what happens.
1) Visit arpazw.gr
2) In the top of page, in search input, write the word "????"
3) Hit search
5) See the results...

Thank you very much for your time