Pressing Tab key shows 'Back to Top' button that does nothing

I created a 'first name', 'last name' 'continue' name input slide. In preview mode, i used the tab key to navigate from one text box to the next text box.

Unfortunately, the tab order is 'first', 'continue', 'last' --(any help with this? re-ordering timeline objects did not help)

While using the tab key, a 'Back to Top' button appeared on my slide. Pressing the button does nothing, except when pressed it disappears. There is no such function in my timeline. 

See attachment.

In fact, using the tab key on any slide during preview scene or slide produces this same 'Back to Top' button, that when pressed, does nothing and disappears. 

What is happening?, and how do i eliminate this function from my project?

Please advise.