Tracking the coordinates of a drawn box on an axes in a GUI

I'm trying to make a GUI which plots data and allows the user to draw a box to zoom in on specific parts of the data. The code is based off of Matt Tearle's code found here. The issue I'm facing is at the end of the code when adjusting the plot's axis limits. The Y limits are not being stored, even though the X limits change accordingly.

 %set the button down callback
 set(plotFig,'windowbuttondownfcn',@startDraw)
 uiwait(plotFig)

    function startDraw(src,~)
        set(src,'pointer','crosshair');

        %get the current point
        cp = get(currentAxes,'currentpoint');

        %loads the initial point and makes variables for opposite corner
        x1 = cp(1,1); y1 = cp(1,2); x2 = []; y2 = [];

        %draws the four sides of the box
        top = line('xdata',x1,'ydata',y1,'color','k','linewidth',1);
        bot = line('xdata',x1,'ydata',y1,'color','k','linewidth',1);
        left = line('xdata',x1,'ydata',y1,'color','k','linewidth',1);
        right = line('xdata',x1,'ydata',y1,'color','k','linewidth',1);

        %set callbacks for motion and button up once button down runs
        set(src,'windowbuttonmotionfcn',@moveDraw);
        set(src,'windowbuttonupfcn',@endDraw);

        function moveDraw(~,~)
            %gets current cursor location
            cp = get(currentAxes,'currentpoint');

            %stores the other corner, first corner is fixed
            x2 = cp(1,1); y2 = cp(1,2);

            %sets the axes
            set(top,'xdata',[x1 x2],'ydata',[y1 y1]);
            set(bot,'xdata',[x1 x2],'ydata',[y2 y2]);
            set(left,'xdata',[x1 x1],'ydata',[y1 y2]);
            set(right,'xdata',[x2 x2],'ydata',[y1 y2]);

            drawnow
        end

        function endDraw(src,~)
            %removes the callbacks. this function is supposed to only run once
            set(src,'pointer','arrow');
            set(src,'windowbuttonmotionfcn',[]);
            set(src,'windowbuttonupfcn',[]);
            set(src,'windowbuttondownfcn',[]);

            %this is the part which errors. y1 and y2 are 0 and 0, which causes
            %the function to error. their actual values are not 0 and 0.
            axis(plotHandles.zoomCutData);

            uiresume(plotFig);
        end
    end

I'm not sure why I can't get the data to be passed between the three callbacks. Even stranger is that x1 and x2 are available in endDraw(), but y1 and y2 are not. x1 and x2 display the correct values.