frame : contentbottom1

If a jump link is used to open in an iframe, the iframe needs to be present... if it's not, the page will open in a blank window. This can happen if a new page is loaded into the frame which holds a page with iframe -> iframe disapears, any jump to this iframe will "fail" and open blank window

This you can see if you load any other page then this page containing the <iframe> into this frame contentbottom1. As soon as you see any other page in this frame, the links to iframe will open a blank window. Click in menu "P3 contentbottom1" and then "P1 iframe"... it will open Page 1 in a blank window