Yes, I noticed that as well.
I just had a look: The problem is the main SVG background image. What's weird is that we had the same problem with Firefox, but the other way around ... We used to have the main background image as a CSS gradient, but because of a bug in Firefox, it was unusable because it was slowing everything down (see FS#2447
). So, we changed the background to use an SVG with a gradient instead. It seems Opera is buggy there and cannot handle it.
But the good news is: Having both, first the SVG and then the CSS gradient, fixes the issue in both Firefox and Opera. So, I'll do that.