@nokesi Due to the feature being so common in many browsers most people are acquainted to it.
I was looking through the forums and found many people asking about the same feature and reporting it as a bug or trying to find the setting.
Also, I haven't been using Opera One, I swtiched to GX instead. It doesn't open a new tab if a tab is closed or moved to another window. So yeah that's the usual behaviour for most of the browsers out there.
It's just a suggestion to improve the user experience for most people 🙂