Strange button in the corner of the fluid box

[hagstrom77]

I built a responsive drag-and-drop interaction with fluid boxes. When I publish or preview, strange little button appears in lower bottom corner. How to get rid of it? It doesn't do anything usefull AFAIK. 

This is the button that I'm talking about:

[Lilybiri]

That button appears when there is not enough space to show all the text.