See the tip scrollposition if your browser goes back at the top of the page when you hit the back button and the tip dom.disable_image_src_set if toolbar buttons of the edit window do not appear.
Opera has some problem with the font Verdana. See this forum post. I'm not sure how to avoid this. Not using Verdana wouldn't be a very good idea as it is the best sans-serif font available I think. I wasn't able to reproduce this on a Windows system, so it seems to be a Linux specific problem.
Verdana is a font provided and owned by Microsoft. Likely the font being used as a replacement is bad in some way, either inherently or in the way it is utilized or rendered.
There seem to be no problem at all with Opera 8.0 on Windows and Linux. All CSS features work correctly, the only exception being opacity of the bottom buttons, but it isn't standard CSS.
You need to set the broken redirect option in the menu (Setup→Network Options→HTTP Options→Broken redirect 302). This enables the redirect behaviour as seen in all major browsers even if it isn't standards compliant.