I have not heard of that. I am cooking black beans today. I soaked them for two days - because I had stuff going on and could not cook them yesterday. I rinsed them and replaced the soaking water quite a few times yesterday. When I picked up the bowl today to rinse again, bubbles came up. Then when I boiled them, there was no foam to skim.
I am cooking them with fennel. I will see how they turn out.