Something in my code is hindering the display of CSS pages on my sites. I need to hit Author Mode twice in order to get the pages to display...once to render ANY page element at all, and once to render any CSS styles. This seems only to be a problem with certain pages I've been testing :: and only with Opera 7. Page style settings are at their default.
Yes, I've seen something similar, but I didn't take the time to explore it fully. What you describe is in the same rough territory, but a bit more extreme.
I see a loss of CSS when I switch back and forth between "small screen" on the View menu. It always takes a Refresh or two to get all the code to render after I return to normal from Small Screen. That "author mode", "user mode" page also gives me some very funny stylesheet behavior when I change settings.
Opera 7 is definitely a beta, with lots of new core features, but lots of funny bugs as well - so I'm not using it for any serious testing yet.