As mentioned in an earlier blog post of mine, they chnged from syncronious Mail database loading to asyncronious Mail database loading which causes that one has to wait 5 Minutes or longer (on a very large database!) sometimes until everything is ready.
As mentioned by burnout426 in this forum thread this changed now:
http://my.opera.com/desktopteam/blog/2012/06/28/more-fixes-for-opera-12> has a Load Mail Databases Asynchronously option that you can uncheck to restore the synchronous behavior Opera had in 10.10 and before.I have tried it by myself and it works pretty flawlessly for me. Since it's a Opera Next feature it cannot be said whether this is a temporary or permanent feature.
While that works for me, the UI is not showing for me for ~5 seconds when Opera starts up while in 10.10 with the same situation, the UI shows instantly. So, it doesn't emulate 10.10 behavior perfectly (for me at least). But, I'll take the 5 second UI block over the slow database loading any day.
Technorati Tags: Opera, mail