Tabs with rounded corners on Windows 8
The problem appears when Opera (26, stable) is opened by another program (e.g. by clicking on a link in another email program).
When Opera has been running before, the opened tab looks as usually on Windows 8.1 (x64), but if it is started by this other program the tabs have rounded corners (like they are on Windows 7 or Opera 12 had).
I've seen someone posting a similar issue on the 28 developer blog post, but since this appears in stable as well, maybe someone else can confirm?
Do you have any switches on the command line in the shortcut you normally use to run Opera?
If so, they won't be used if Opera is run from another program, as that will use the command line that's in the registry for that file association.
That could account for the difference you're seeing.
Thanks for the answer. Basically I didn't mess with the startup switches
That's why I started wondering. I had seen this very sporadically in earlier versions as well (on another PC). I could now finally figure out where it comes from and reproduce it "reliably".