I found the difference.
When I select the text, I click and drag the mouse from right to left (maybe left to right also works :-) ). Notice when you do this, the text while dragging is turning blue, but when I release the mouse-button it turns to light-grey. In your screencast it says blue...
I've attached a gif showing how this works...
I'm using here:
Microsoft Edge 40.15063.0.0
Microsoft EdgeHTML 15.15063