I'd think so too --- what would be the purpose of such a code, anyway? The purpose of the location header is to direct the browser to the scene of the action, or away from some action the surfer's not supposed to see (it's oft used, for example, to move a user away when not authorized....)
Spawning new windows is a client activity; have your PHP send some JS to the browser...I don't have my JavaScript book lying around here, but it should be a matter of just 2-3 lines, or even less...