imshow appears to interfere with ButtonDownFcn

In the following code, if ShowImage is set to false, a mouse button press causes ax_bdfcn to be called. However, if ShowImage is set to true, mouse button presses do not seem to have any impact.

function ShowButtonDownFcnIssue()

close all
ThisImage = imread( 'board.tif' ) ;

figure(1)
ShowImage = true;
if ShowImage
    h=imshow( ThisImage ) ;
    hold on
    set(h, 'HitTest', 'off' );
end

plot( [149 136 ] , [248, 204  ] , 'c', 'LineWidth', 5, 'HitTest', 'off' );
hold on

axes_handle = gca;
set(axes_handle, 'HitTest', 'on', 'ButtonDownFcn',{@ax_bdfcn});
pause( 25 )

% call back as nested function
    function ax_bdfcn(varargin)
        disp('INTERRUPT')
    end  % close nested function
end