Tab rendering broken on Win7 with x64 version

[aguenther]

As soon as I open a second tab, the tab bar just turns white. Clicking around makes it look like the tabs are rendered far too wide.
On the x32 version, the tabs are visible, but quite ugly, and without text.
Using Win7 x64, with classic shell and the classic theme (the one which makes win7 look like win98)

screenshots:
64: http://files.katzenpapst.de/files/asd1.png
32: http://files.katzenpapst.de/files/as2.png

[cbucher]

In Windows 7, basic themes don't use DWM neither uxtheme ...
there use slow software rendering
I just have fixed rendering but I will not support this themes!