white screen on boot right before login promt

[alx]

Power on or restart the machine.
Right before the login promt appears the screen goes white.
Then i have to click once anywhere on the screen .
After clicking , white screen dissapears and i can see the login promt and log normaly.

lsb_release -rd
Description: Ubuntu Vivid Vervet (development branch)
Release: 15.04

apt-cache policy xorg
xorg:
  Installed: 1:7.7+1ubuntu8.1
  Candidate: 1:7.7+7ubuntu3
  Version table:
     1:7.7+7ubuntu3 0
        500 http://gr.archive.ubuntu.com/ubuntu/ vivid/main amd64 Packages
 *** 1:7.7+1ubuntu8.1 0
        100 /var/lib/dpkg/status

Bug Report guidelines 3 & 4 : Obviusly the white screen shouldnt be there and i should be able to see the login promt.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: xorg 1:7.7+1ubuntu8.1
ProcVersionSignature: Ubuntu 3.19.0-9.9-generic 3.19.1
Uname: Linux 3.19.0-9-generic x86_64
ApportVersion: 2.16.2-0ubuntu2
Architecture: amd64
CurrentDesktop: XFCE
Date: Fri Mar 13 14:34:52 2015
EcryptfsInUse: Yes
InstallationDate: Installed on 2015-03-02 (10 days ago)
InstallationMedia: Xubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140416.2)
SourcePackage: xorg
Symptom: display
UpgradeStatus: Upgraded to vivid on 2015-03-02 (10 days ago)

[Pavel Roskin (proski)]

It is a duplicate of the bug 1428884. The title of that bug not good - "Xorg crash", even though no crash is described. Anyway, the symptoms are the same.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.