Weird behavior of JitterMatrix

In my java external application I am drawing into JitterMatrix using jit.gl.sketch then display the JitterMatrix in a window. My order of operations are;

(1)Draw some stuff using sketch to JitterMatrix
(2)Change the pixels in JitterMatrix
(3)Draw more stuff using sketch to JitterMatrix
(4) send the JitterMatrix to window

Logically I expected that (2) will change what I have drawn in (1) , then on top of the changes (3) will appear without any affect from (2)
But what I see is (3) is completely missing ????? only (1) and (2) working ...
But If I comment out (2) I can see everything is drawn properly
Can anyone explain what is happening here ???????????