Sometimes but not rarely when I copy/paste a word into the search bar,
I have an alternative theory, but I may be wrong:
Opera uses Ctrl+Shift+V as default keyboard command to call up a web page being in the clipboard comfortably immediately.
If you use this key combination sometimes inadvertently instead of just CTRL+V, depending on what is currently in the clipboard, this phenomenon could possibly be triggered.
To check, change or delete that keyboard shortcut, open Opera's preferences and search for Paste and go.
since a few days I am really fed up with sync.
It doubled my bookmark folders and some speed dial folders.
Some of the latter are empty or don't contain as much links as the original.
Annoying is that I don't know which bookmark folders are corrupted, while the defective speed dial folders are easy to recognize.
So I going to empty all and use firefox instead.