Been using Opera quite extensively for awhile and keep a hefty number of tabs open generally at all times and have them sorted based on their window. For this reason I love the delay loading of background tabs because I'm not looking to always have every tab running eating tons of processing power. The issue comes into play with multiple windows open. The feature seems to malfunction on any window beyond the first. Almost more of a bug with it, if you will. This can become quite cumbersome for windows with music or videos when I load up their windows and have to let them all load and then stop them from playing and then have them still constantly be a drain on my memory and cpu just by being open.
All in all thanks for the wonderful browser and taking the time to read this suggestion.