1. Disconnect from the Internet and then install Opera
2. Delete "Opera scheduled Autoupdate [random numbers]" from Scheduled Tasks (Task Scheduler in Windows Vista and newer)
3. Go to "\Program Files\Opera\36.0.2130.65" and delete the following files: 
opera_autoupdate.exe
opera_autoupdate.licenses
opera_autoupdate.version
4. Reconnect to the Internet and after opening Opera for the first time, go to "opera://flags/?search=smooth-scrolling" and press the "Disable" button