I replaced my dell laptop with a Surface Pro (Windows 8.1), but I have found strange behaviour when I use it connected to large external displays (50") , using a MS display port VGA adaptor. I have an Excel 2013 worksheet with some buttons on it that call some macros, when external display is disconnected, everything works as expected. But when connected clicking on a button linked to a macro, it causes the text in the button to increase in size and macro does not run. Clicking button again causes text to grow again and macro does not run. The display port adaptor is a Microsoft one and I have tested using another one, but with the same results. I am assuming it is a driver issue, but I use the Surface on customer sites,I do not have any possibility to change drivers. Any thoughts on this problem?