However, if you make any edits to a post on DW that is not locked, your LJ settings will change accordingly. When I was cross-posting, how I avoided that was by forcing myself to check the cross-post box every time I wanted to cross-post.

Thank you for letting me know.

I'll have to check it out because jenett seems to contradict you above on this point specifically. But, if you're right I imagine that not setting crosspost as default will help.