I can confirm this behavior and the initial black behind the Dash is due to the fact that OpenGL 1.4 is being forced as the workaround for the poor performance for Mesa 9.2. Why it takes changing the background to get the correct blurring still needs to be investigated.
I can confirm this behavior and the initial black behind the Dash is due to the fact that OpenGL 1.4 is being forced as the workaround for the poor performance for Mesa 9.2. Why it takes changing the background to get the correct blurring still needs to be investigated.