As of having upgraded xfce4 to 4.2.1, the panel does not appear to save its
configuration at all. After login, it always pops up with default configuration,
at the lower border of the desktop.

I have taken a look into .config/xfce4/panel, and there are two files: 

contents.xml.active
contents.xml.bak

contents.xml.bak contained my original settings so (after making an extra backup
copy for good measure) I copied them to contents.xml.active - to no avail. I
then noticed that there was only a contents.xml.bak after logout, so I copied
the backup (of contents.xml.bak) over the present contents.xml.bak file - again,
to no avail.

I then downgraded to xfce4-panel 4.2.0 and copied the backup to contents.xml.
And Io, there was my panel configuration again.

I am using Gentoo Linux (~x86), and these are the packages that got downgraded
along with xfce4-panel:

xfce-base/libxfce4util-4.2.1
xfce-base/libxfcegui4-4.2.1
xfce-base/libxfce4mcs-4.2.1
xfce-base/xfce-mcs-manager-4.2.1
xfce-base/xfce-mcs-plugins-4.2.1
xfce-base/xfce4-panel-4.2.1

So, I'm not quite sure whether this is indeed a panel bug or a bug in some of
the other packages.

Please tell me if you need more information.

Reproducible: Always
Steps to Reproduce:
1. Login to xfce 4.2.1
2. Customize panel
3. Logout and Login again

Actual Results:  
Customizations of panel are gone.

Expected Results:  
Customizations of panel should have been saved.