I am a member of a Chabad-Lubavitch shul with its wonderfully diverse community here in Southeast Asia though I am not a Chasid. I may have caused some discomfort to our much loved Rabbi & Rebbetzin to whom I wished mazel tov on the birth of their daughter's first-born son. The Rebbetzin told me in a soft and polite way that wishing someone mazel tov in this kind of situation was not part of their tradition (Chasidic?). I was concerned that I had made a gaffe. This happened during a Friday-night kiddush at the shul, the mother and newborn still hospitalized, awaiting their hospital discharge.
Why is this so?