Yep, it happens... because those people chose to be that way.
You are who you are.
If you're deaf and you have a deaf friend who is very close with you. One day, he gets CI and suddenly changes his personality... you shouldn't blame the fact that he got CI. You should blame the fact that he chose to change and not talk to you any more. Therefore, he's not a true friend. Let him go.
If this was said 7 months ago, I would have said impossible, but know I can see this happening. When I first got my CIs I was so excited, I wanted to share it with a teacher who is deaf at my school. She is not able to get a teaching job even with a master's degree because of her hearing. She wears one aid and you she uses ASL. She works as an assistant and runs our computer lab.
At first I think my peronality changed as well. BUT....I kept from saying anything to her except our normal conversations. She sent me a card at Christmas saying how happy she was for my hearing gain. It made me think, she is really happy for me and my choice. And you know what I am really happy for her choice. We may chose different path but we enjoy each other and our friendship. I don't need to put my CIs on anyone.
Sometimes it is a process of keeping your mouth shut and realizing my personal choice is that mine.