I have the same problem. Tabs load only when I click on them instead of being loaded at Opera startup. I have some 30 tabs open and I would like them to open at startup.
I also experience a problem when tab is loaded already. When scrolling down the content of the tab loads when showed on screen. Further I scroll down more of a content loads. I would like whole tab to be loaded when I open it. Not start loading after I scroll down. I don't know, maybe this is another issue but I just thought it's worth mention it.