AFAIK the Unity side panel should not appear in either of the flashback sessions.
Ubuntu GNOME uses GNOME Shell as the default DE but also offers a Classic session at login. That Classic session is in no way related to flashback or gnome-panel though.
If you're fully updated you might be able to gain a bit by renaming some of the hidden dots in home:
Code:
lance@lance-desktop:~$ ls -a
. .dbus .ICEauthority .profile
.. deja-dup .local Public
.adobe Desktop .macromedia Templates
.bash_history .dmrc .mozilla .thunderbird
.bash_logout Documents .mozilla_BK Videos
.bashrc Downloads .mozilla_OLD .Xauthority
.cache examples.desktop Music .xsession-errors
.compiz .gconf newegg_20140307.pdf .xsession-errors.old
.config .gstreamer-0.10 Pictures
Possibly .compiz, .config, .gconf, and .local - then rebooting
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