Inkscape returns a warning when its manual is closed

[Alberto Salvia Novella]

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HOW TO REPRODUCE
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1. Go to the "Help / Inkscape's manual" menu.
2. Close the opened manual.

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BEHAVIOUR
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- EXPECTED: Nothing else to happen.
- REAL: A warning message is returned.

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MESSAGE CONTENT
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(process:7318): GLib-CRITICAL **: g_slice_set_config: assertion `sys_page_size == 0' failed
** (firefox:7318): WARNING **: Failed to find domain member of JSON manifest
(firefox:7318): LIBDBUSMENU-GLIB-WARNING **: Translation has an invalid value 'I-->D' for default text direction. Defaulting to left-to-right.

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: inkscape 0.48.4-0.1ubuntu2
ProcVersionSignature: Ubuntu 3.8.0-21.32-generic 3.8.8
Uname: Linux 3.8.0-21-generic x86_64
ApportVersion: 2.9.2-0ubuntu8
Architecture: amd64
Date: Thu May 23 17:50:38 2013
InstallationDate: Installed on 2013-05-21 (2 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: inkscape
UpgradeStatus: No upgrade log present (probably fresh install)