Forum threads lost in a void?

since the admin's corner is locked and i'm unable to connect to efnet, i'm
posting this here.

when i enter the forum (http://www.eztvefnet.org/?forum=index) it displays a
list of threads, nothing unusual there.

when i click the little arrow on the bottom to bring me one step forward, it
brings me to http://www.eztvefnet.org/?forum=index&cp=22 .

however, if i, after doing this, click the arrow to move backwards (the one on
the bottom, not the browser one) it brings me to
http://www.eztvefnet.org/?forum=index&cp=21 | which does not contain the same
threads as http://www.eztvefnet.org/?forum=index or
http://www.eztvefnet.org/?forum=index&cp=22 .

i'm aware url:s aren't allowed here, but i needed them to illustrate the problem.

just to word what pqed said in another way:
basically the arrows take you forward to the third page... and then you have to
go back one to get to the real second page..
then you have to click forum to get back to page one again, because on page two
the arrows are gone...