Blank screen after screen locked

[Biji]

After returning from locked screen, only blank screen shown instead lock screen background image. I have to press Esc several times to enter to unlock screen

someone also report it but expired: #1207292

Thanks

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: gdm 3.16.1.1-0ubuntu1~vivid2 [origin: LP-PPA-gnome3-team-gnome3-staging]
ProcVersionSignature: Ubuntu 3.19.0-30.34-generic 3.19.8-ckt6
Uname: Linux 3.19.0-30-generic x86_64
NonfreeKernelModules: fglrx
ApportVersion: 2.17.2-0ubuntu1.5
Architecture: amd64
CurrentDesktop: GNOME
Date: Sat Oct 17 05:13:07 2015
EcryptfsInUse: Yes
SourcePackage: gdm
UpgradeStatus: No upgrade log present (probably fresh install)
modified.conffile..etc.gdm.greeter.gsettings: [modified]
mtime.conffile..etc.gdm.greeter.gsettings: 2015-09-18T11:04:41.192714
upstart.gdm.override: manual