i'm pretty sure that the default set-up for FCP is NTSC DV,
so that would explain why it would have switched to that.
it can pay to create a set of preferences that you store and use as a "default" for when you have to trash them again.
there are a few preference manages around that can help you with all that,
check out lafcpug moderator Jon Chappell's company Digital Rebelion:
[
www.digitalrebellion.com]
you can also manage your prefs manualy.
read this old, but not out of date (this week) article:
[
www.lafcpug.org]
cheers,
nick