Folder icon is incorrectly thumbnailed if the source of the icon has been updated

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STEPS TO REPRODUCE
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1. Download an image into a folder.
2. Change folder's icon to the downloaded image.
3. Overwrite the image with a new one.
4. Change folder's icon to the new image.

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EXPECTED BEHAVIOUR
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The icon to change to the new image.

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REAL BEHAVIOUR
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The icon doesn't update.

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: nautilus 1:3.6.3-0ubuntu16
ProcVersionSignature: Ubuntu 3.8.0-19.30-generic 3.8.8
Uname: Linux 3.8.0-19-generic x86_64
ApportVersion: 2.9.2-0ubuntu8
Architecture: amd64
Date: Tue May 14 12:27:29 2013
GsettingsChanges:
 b'org.gnome.nautilus.window-state' b'maximized' b'true'
 b'org.gnome.nautilus.window-state' b'sidebar-width' b'220'
InstallationDate: Installed on 2013-05-12 (1 days ago)
InstallationMedia: Ubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
MarkForUpload: True
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=es_ES.UTF-8
 SHELL=/bin/bash
SourcePackage: nautilus
UpgradeStatus: No upgrade log present (probably fresh install)