lock-screen active but invisible with dual-monitor

OK, So I went out for a walk for 30mins and left my computer unlocked.

It's set to turn off the screen after 10mins and then lock it. And show the login prompt when I go to use it.. you know.

So I get back and the screens are NOT off and the primary screen is on and all my stuff can still be seen. But my secondary screen is locked and black.

I cant click anything on the primary screen so I guess the lock screen is there, but I cant login like I do later in the video. I try some keyboard short-cuts and accidently drop to tty0 and then back to tty7, now the screen is black and I can see the mouse SO i assume the login-box IS there I just cant see it as when I hit ESC the mouse vanishes which is usually how the lockscreen works.

SO i click, type in my password and hit enter and w00t its unlocked. No idea why it did this.

Video of trying to get in when I got back: http://youtu.be/TPjzCl7MDj0

ProblemType: Bug
DistroRelease: elementary OS 0.2
Package: elementary-desktop 1.299-0~373~precise1 [origin: LP-PPA-elementary-os-daily]
ProcVersionSignature: Ubuntu 3.5.0-28.48~precise1-generic 3.5.7.9
Uname: Linux 3.5.0-28-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu17.2+elementary3~precise1
Architecture: amd64
CrashDB: elementary_meta
Date: Sun May 12 16:18:09 2013
InstallationMedia: elementary OS 0.2 "Luna" - Beta 1 amd64 (20121114)
MarkForUpload: True
ProcEnviron:
 LANGUAGE=en_NZ:en
 PATH=(custom, no user)
 LANG=en_NZ.UTF-8
 SHELL=/bin/bash
SourcePackage: elementary-meta
SuspiciousXErrors:

ThirdParty: True
UpgradeStatus: No upgrade log present (probably fresh install)