EDIT : Replacing opened tabs with the group you are opening is a feature that is disabled by default. You have to enable it in Tabber's settings and can disable it at any time.
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I think you are talking about the button that replaces your group with the tabs that are currently opened.
I'm sorry about this, I agree that it's not clear.
The button was aimed to allow you to quickly replace a group without erasing it then recreating it.
I will improve the behaviour of the button in the next release and make it more clear.
Do not hesitate to suggest any replacement in a edited comment.