Weird behavior on Stained BumpDistord

Hello everyones !

I am pretty new to shaders, I would like to use a one to simply distord what's behind the object it applies to. For that purpose I decided to use "Stained BumpDistort" from the standard assets. I didn't put any picture on the rgb field and I put a normal map on the second one. When everything is fine it behave as follow :



And sometimes for an unknown reasons it show all the surface of the object as bellow :


It seems like it is related to my camera's orientation since if the camera don't move it doesn't "change state".
Does anybody have an idea ?
Thanks !