QPaintedTextureImage alpha with QTextureMaterial incorrect

When QPaintedTextureImage's painter clears to a transparent background and is used with QTextureMaterial, the pixels that should have 0 alpha still show some ambient white color. 

Attached a modified example of the manual test showing this problem.  The clear pixels in the texture should show the bright green color through.  The contents of the texture image don't seem to get cleared correctly when the QPainter background is set to QColor(0,0,0,0), either.