I've never heard of that but I wouldn't be worried about your son's talking skills till he is at least 2yrs old. My son at 18 months didn't say a lot either. He had a few consistant words like M., dada, etc but other than that, he would say a new word for a week and then you'd never hear it again!! At his 18 month check up, his ped said we would wait till he turned 2 to do anything. Let me tell you, by time he was 2yrs, he was right on target with his speech. Now at 2 1/2yrs, he is over developed for his age!! Go figure. She did say that boys do tend to develop speech slower than girls and since he had an older sibling, that could have been slowing him down as well.
Even though he can't really talk back to you, talk to him!! Tell him about what you need to buy at the store while you push the cart. Ask him what he wants for dinner, give him 2 packages of crackers to pick from for his snack, etc. People used to look at me strange when I did that with my kids, but how else are they supposed to learn if we don't encourage them right??!!
Good luck!
S.