button ui becomes active by click outside the button in exe file!!(unity 5.1)

Hi . I have a big problem with button ui in unity 5.1.3/
When I click on the button in editor unity ,it is perfect and correct but in exe file in low resolution(like 800*600) I can click outside the button and button will be active.!!

Is the client full screen? cause i noticed when it’s in full screen all the ui elements mess up for some reason by default, and unfortunately I have not been able to find a solution for this so i just made my client re sizable so at least you can maximize it that way.