I also believe messing with their food actually causes the aggression or at least aggravates it but not with all dogs of course. But I did this with my Golden thinking what you thought and he eventually ended up snapping at me once and getting stiff anytime I came near his food dish... And I did pretty much exactly what you did.
Now I've never messed with my other 3 dogs while they were eating and none of them have any issue with me being near their food and can eat with the other dogs around which my Golden cannot do either, he has to eat in his crate now.
So my view is just leave them be, let them eat and they won't have any reason to guard from you... If you have to mess with them then just ADD high value stuff into the bowl instead of grabbing it away from them. I also practice NILIF so they have to work for their food before they get it but I don't mess with them once they have earned it.
Ollie vom Grunenfeld HIC CGC
Last edited by Carriesue; 08-31-2013 at 05:42 PM.