This. When doing Stable Diffusion, I have noticed this as well. Adding negatives can sometimes lead to the opposite results.

From what I can tell, if you say "no computers" for example (ie adding computer as negative), you are setting the scene for something like "where there should be computer, there is not".

I can't better describe this phenomenom, only that it can completely change the output in unexpected unwanted ways.

AB - B = AC