image processing problems with Simulink

I am developping an image processing algorithm using morphological operators (3x3 kernel based by using flip-flops).

The blocks designed are very close to the Avalon Edge Detector block provided within the DSP development kit.

A problem has been detected, it consist of a movement to the right of 10 pixel in the resulting image and this effect is very bad for my algorithm.

Could you give any trick to solve or remove this colateral effect?