Bottom panel for plugin widgets is not shown

[RaduStoica]

I tried creating a plugin that adds a frame to the MAIN_BOTTOM panel, but it is not shown. Simply changing from MAIN_BOTTOM to MAIN_TOP the widget location shows the frame.

I've attached a simple plugin to reproduce this problem.

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: rhythmbox 2.97-1ubuntu5
ProcVersionSignature: Ubuntu 3.5.0-18.29-generic 3.5.7
Uname: Linux 3.5.0-18-generic i686
ApportVersion: 2.6.1-0ubuntu6
Architecture: i386
Date: Sat Nov 17 08:30:23 2012
InstallationDate: Installed on 2012-09-22 (55 days ago)
InstallationMedia: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release i386 (20120817.3)
MarkForUpload: True
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: rhythmbox
UpgradeStatus: Upgraded to quantal on 2012-09-23 (54 days ago)