Control panel dialogues don't respond to mouse clicks

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WARNING
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- This bug report refers only to the control panel's dialogues being unclickable. For any button not responding, refer to bug #410407.

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HOW TO REPRODUCE
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1. Go to a web-page that uses your web-cam.
2. Switch on the web-cam through the interface provided in the web-page.
3. When you are asked to allow the web-cam to be accessed by Adobe Flash, click on the "Allow" button.

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BEHAVIOUR
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- EXPECTED: The button to be clicked.
- REAL: Its impossible to click any button from the Adobe Flash dialogue that appeared.

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WORK-AROUND
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- To use the online control panel instead, at http://www.macromedia.com/support/documentation/es/flashplayer/help/settings_manager08.html.
- If available; to disable desktop effects, or to switch to Ubuntu 2D desktop at the log-in screen.

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RELEVANT DETAILS
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- Affects any GNOME 3 based desktop environment, which uses 3D desktop effects.
- Doesn't affect Unity 2D, KDE, XFCE and LXDE desktop environments.
- Affects any web-browser.
- Gnash is incompatible with these dialogues too.
- "swfdec-mozilla" is now a dummy package for Gnash.
- Installing the Flash Player from Adobe's web-page has the same effect.

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: flashplugin-installer 11.2.202.285ubuntu0.13.04.1
ProcVersionSignature: Ubuntu 3.8.0-22.33-generic 3.8.11
Uname: Linux 3.8.0-22-generic x86_64
ApportVersion: 2.9.2-0ubuntu8
Architecture: amd64
Date: Sun May 26 18:40:40 2013
InstallationDate: Installed on 2013-05-21 (5 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
MarkForUpload: True
SourcePackage: flashplugin-nonfree
UpgradeStatus: No upgrade log present (probably fresh install)