I have been experiencing the same issue with Opera opening automatically each time I start Windows. It starts each time with three blank Speed Dial tabs opened.
I can add, that when this first started, I ran a Google search to see if anyone else was experiencing a similar issue. I initially didn't find any recent messages, but the consensus of what I did read pointed toward possible malware. While scans showed nothing abnormal, to be sure I restored my C: drive from a backup from about 30 days prior. Once the restore was complete, Windows started without Opera opening automatically. However, once I opened Opera, I received a message that it was updated to the latest version and since that time it launches automatically each time I start Windows.
So, I believe whatever is causing the problem is related to the latest Opera update.