The green maximize button default behavior is to zoom a window into Full Screen mode, this is different from how OS X used to behave where the green button would simply maximize a window. In this brief video, you'll see how to change this behavior by using BetterTouchTool, a free application for Mac. Details in the accompanying article here:
http://osxdaily.com/2015/03/11/change-the-green-button-maximize-behavior-in-os-x-yosemite-with-bettertouchtool/
Alternatively, you can use the old style Green Button behavior by Option+Clicking the green button as described here:
http://osxdaily.com/2014/10/28/maximize-zoom-windows-os-x-mac/
