I don' know, but the bug can reproduce every time
Open designer(zh_CN version4.7.0),
drag and drop one form(must need qrc file ) to window. Now pop up a messagebox: "loading qrc file". Then if I clicked "Yes" button, the window crash., or if I switch other windows, the messagebox not respose, must kill it in "windows Task Manager".
So this problem I met is not the same to "Multiple pages in QStackedWidget":http://developer.qt.nokia.com/forums/viewthread/4293. If not loading qrc file, I can open more than 15 files