Unity launcher greys out if Firefox tab or marked text moved over it

[Colin Law]

Using up to date Raring alpha. To replicate:
Set the Unity launcher auto-hide Off.
Open Firefox with multiple tabs.
Drag one of them over the Unity Launcher (no need to drop it).
The launcher immediately greys out except for the Nautilus icon and does not recover.
The launcher icons continue to work but are greyed out.

This may seem like an unusual thing to do, but with dual displays with the launcher on the right hand display the problem is seen when dragging a tab from one display to the other, as it crosses the launcher.

Edit:
I am also seeing the same greying out if I mark some text (in Tomboy Notes for example) and drag it over gedit in the launcher.

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: unity 6.12.0daily13.02.19.1-0ubuntu1
ProcVersionSignature: Ubuntu 3.8.0-7.15-generic 3.8.0
Uname: Linux 3.8.0-7-generic i686
ApportVersion: 2.8-0ubuntu4
Architecture: i386
CompizPlugins: [core,composite,opengl,compiztoolbox,decor,vpswitch,snap,mousepoll,resize,place,move,wall,grid,regex,imgpng,session,gnomecompat,animation,fade,unitymtgrabhandles,workarounds,scale,expo,ezoom,unityshell]
Date: Sat Feb 23 10:18:32 2013
InstallationDate: Installed on 2012-08-01 (205 days ago)
InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Alpha i386 (20120730.1)
MarkForUpload: True
SourcePackage: unity
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

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