Yeah, it is so common. Don't worry too much. I have met loads of kids in childcare who hardly talk in care, but are real chatterboxes at home. Occasionally you can "catch" them when they don't think anyone from childcare can see/hear them, and hear them nattering away
Most do eventually warm up - don't forget that you've had since birth to have gained your child's trust. People at childcare, no matter how early they start, are 8 months [in your case] behind. No wonder, really, that he talks more with you.