it is not a problem with the browser cache, it is a different behaviour if pgadmin is startet in the addressline oft he browser or via link clicking from an other site.
If document.referrer is empty then Query tool can start in another browser tab.
If document referrer contains another hostname then a cross site scripting police prevents access to javascript code in an other tab.
I am not a web developer but i think this has to be fxed in .html or .js code.