Shift in trajectory of data points plotted after using imshow and hold on

Hello all I have encountered a weird problem today. The Final trajectory of the static points plotted after using imshow,hold on and without using imshow hold on are different.Why is this happening?. Kindly help.Below is the code i have used.

x=[100,200,300,400,500];
y=[100,200,300,400,500];
a=uint8(zeros(600,600));
imshow(a);hold on;title('with imshow')
plot(x,y,'wo');

figure,plot(x,y,'bo');title('without imshow')