9.0-RC2 - bsdinstall overwrites /etc/fstab and spams /etc/rc.conf after edits in shell

Fresh install of 9.0RC2.
Which comes first the, installer writing config files, or user using live
shell to write custom config files?

On the "Final Configuration' screen I have the option to change several
options like hostname/root password/network/etc.etc and final option is:

"Open a shell in the new system"

I used that option to create /etc/fstab with /dev/gpt/label for my
partitions.
After I reboot, my 'fstab' changes were overwritten with the installer
/dev/ada0p# devices.

Another file I tested is '/etc/rc.conf' - it just gets appended and the
'hostname=' entry is added on the very first line, so my entries stayed in
the middle.

I understand "Open a shell in the new system" is with the config files
already written and are 'editable' but that is not the case. What else is
touched in that final 'Exit' that will overwrite changes made in 'shell' ?

How about adding that option into the last 'Complete' dialog where the
configs are all written and are safe to edit and have three options:

<Reboot> <LiveCD> <Open a shell in the new system> ?

]Peter[
  Just a complain...errr...tester.