I am getting a white screen after startup in Lubuntu 15.04 and I do not know if this is by design or if it is a bug. It clears away from a mouse click to reveal the login window. It reminds me of the Windows 8.1 start screen which acts in a similar way, though I have no idea why it would be a white screen with mouse cursor - it just seems wrong.
I got this in Lubuntu 15.04. It appears to be an issue with
Unfortunately, the PPA for the fix in that post is not available anymore.
It appears to be available here:
The good news is that the fix is supposedly included in 15.10, which should be releaed in a few weeks.