When using two displays extended vertically rather than horizontally (eg, Display 1 arranged to be above Display 2 rather than to the left or right of), if a dialog drop down is longer than can be fit on one of the displays and is positioned in screenspace such that it should spill onto the other display, it is cut off at the edge instead. Screenshot attached. Running latest OS X and latest InDesign CC. Only occurs in dialogs: parent window drop downs don't try to extend beyond the active display.