I try to use vertex painting in cycles as a factor to mix two different materials, which works perfectly fine. However, while I paint the object in the viewport in rendered shading mode, the viewport window only updates when I change the viewport shading mode or the object interaction mode (I resorted to pressing tab twice after a brush stroke as a "solution").
On the other hand, when I use a texture as a mix factor in texture paint mode, the viewport window in rendered shading mode updates immediately after I release the mouse button.
In this video (at ca. 1:39) which shows the same node setup as mine, you can see that the viewport updates without the user having to change the shading mode or the interaction mode.
Which settings or addons do I have to use to get the viewport to update in real time?
I checked the following Blender versions for Windows and the problem appears in the Windows versions 2.65(64bit), 2.68(64bit), 2.72b(32bit/64bit) and 2.73(32bit/64bit).
It doesn't appear in the Windows versions 2.63(32bit/64bit) (the same version as in the linked video), 2.64(64bit) and 2.64a(64bit).