Why safari.extension.globalPage can't receive message from safari.self.tab.page?

Question

I set up a popover, when it has been showed, click a button in it for creating a new tab to show a seetting page for my extension,

and in the seetting page, I sent a message:

safari.self.tab.page.dispatchMessage("userAndPassword",info);

but the golbal page (safari.extension.globalPage) can not receive the message,

although I had did:

safari.application.activeBrowserWindow.addEventListener("message",handleSettingActionFromTab,false);
safari.application.addEventListener("message",handleSettingActionFromTab,false);
//safari.application.activeBrowserWindow.activeTab.addEventListener("message",handleSettingActionFromTab,false);


window.addEventListener("message",handleSettingActionFromTab,false);
safari.extension.globalPage.contentWindow.addEventListener("message",handleSettingActionFromTab,false);
//window.safari.addEventListener("message",handleSettingActionFromTab,false);

Fortunately, the popover page can receive the message but I want to know why the golbal page can not .

Thanks very much.