[arch-general] gnome-shell - massive cpu usage in dual screen mode

Hi, I installed gnome3 from testing today, and it works fine so far. But in dual screen mode, the gnome-shell uses between 50 and 100% cpu continuous. Just after login, without any other programs running. If I switch off one of my displays - it does not matter which one, the laptop display or the vga plugged - gnome-shell runs on 1% cpu usage again. It is also possible to switch between the displays without problems, as long as one of them is switched off. Since this is a 6(?) year old Intel 915GM chipset, it's maybe just related to too little grafical power. Is anyone able to confirm this on a more powerful machine? -- chris