Browser: Opera 47.0.2631.71, developer tools toggled on
System: Mac OS X 10.12.6 64-bit
Reproducible on a non-premium account, plain V3 (no beta).
Baseline network activity summary after turning on the Opera's built-in ad blocker, and clearing the browsing data other than the passwords and cookies: 59 requests, 757kB transferred, DOM content loaded in 1.78 sec, finished loading the page in 2.28 seconds.
So far so good.
Now unblock the ads, reload the page. While the page reloads reasonably quickly, it keeps downloading something without any visible effect. about 2 minutes later, the cooling fan comes on and my macbook is getting hot. There seems to be no way to stop the incoming data (the relevant control in Opera flickers between X and reload symbol).
After about 4 minutes, the network summary indicates having handled some 6,300 requests, and about 32 MB downloaded.
After another 4 minuters, the request count is about 12,300, with 46.4 MB transferred; the largest pieces of data are https://www.hbd-cm.com/vid/These_sisters_convinced_the_Bali_govt_to_ban_plastic_bags.mp4 (twice!), https://www.hbd-cm.com/vid/Meet_The_Creator_Of_Coconut_Jerky_Startup.mp4, and some other video crud that was not even visible in my window.
Somewhat disturbingly, opera indicates having blocked content from insecure sources. Looking at the console log, it mostly complains about http requests that should've been served via https, but since there are about 1300 errors reported, it is not clear whether that's all that is to it...
Seriously, guys, this kind of uncontrollable bandwidth hijacking is not acceptable...