I have found some odd behavior with Panel 2 (the 'dock' panel).
On at least two occasions it just disappeared (forced a reboot/restart of X) and wouldn't appear when I moused in that direction.
One of these occasions it was on the left, Panel 1 at the bottom. I shuffled things around, moved Panel 1 back to the top, Panel 2 to the bottom. About a week later, Panel 2 failed to appear again, again forcing a reboot/restart of X.
I opted to leave things top-and-bottom due to having them bottom-and-left causing issues trying to access the menu button for Panel 1 (Panel 2, despite not being big enough to need it, would appear when I moved to the left, and sit infront of the button for Panel 1's menu, making a very small click area available... I opted to change my user habit instead and go back to something resembling default layout)
Most recently the issue I had was that Auto-Hide would't work. The 'dock' remained up, and over the top of my status bars and text etc. Going into Panel Configuration and turning off 'auto hide' would resize my applications not to sit underneath the panel, but toggling this wouldn't fix it. Restart/reboot required.
markf@hawkeye:~$ lsb_release -rd
Description: Ubuntu precise (development branch)
Release: 12.04
markf@hawkeye:~$
markf@hawkeye:~$ apt-cache policy xfce4-panel
xfce4-panel:
Installed: 4.8.6-2ubuntu2
Candidate: 4.8.6-2ubuntu2
Version table:
*** 4.8.6-2ubuntu2 0
500 http://archive.ubuntu.com/ubuntu/ precise/universe amd64 Packages
100 /var/lib/dpkg/status
markf@hawkeye:~$
I wondered if the disappearing panel was related to https://bugs.launchpad.net/ubuntu/+source/xfce4-panel/+bug/53897 .
However the Panel refusing to auto-hide may be a different issue.
ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: xfce4-panel 4.8.6-2ubuntu2
ProcVersionSignature: Ubuntu 3.2.0-17.27-generic 3.2.6
Uname: Linux 3.2.0-17-generic x86_64
ApportVersion: 1.95-0ubuntu1
Architecture: amd64
Date: Thu Mar 29 11:10:57 2012
InstallationMedia: Xubuntu 12.04 "Precise Pangolin" - Beta amd64 (20120228)
ProcEnviron:
LANGUAGE=en_NZ:en
TERM=xterm
LANG=en_NZ.UTF-8
SHELL=/bin/bash
SourcePackage: xfce4-panel
UpgradeStatus: No upgrade log present (probably fresh install)
Status changed to 'Confirmed' because the bug affects multiple users.