I too have this same annoying issue.
Youtube and other webpages with flashplayers on them used to start automatically. Now even in Settings-Webpages and put it on Recommended which is Autostart, it just WONT start on its own.
Opera, sorry but this Opera 15 and based on Chrome is a huge let down, not to mention no longer a in-browser email system. Looks like I might as well just go use Chrome again.
But now in Opera 15, these issues are fixed, but the new ones are more annoying.