Actually, this feast was imported late by the Latin church from the Byzantines. Its origins are supposedly in the 400s, when a man heard angels singing happy birthday to the Virgin Mary. It is a day of veneration, but this story is considered apocryphal. I also know that the immaculate conception of Mary is one of the two infallible statements that the pope has ever made (the other concerning the assumption of Mary). Notinally, papal infallibility is a more credible concept when it is sparingly exercised, and only with regards to faith.
When I think about feasts such as this, I always wonder what the house looked like. Was the roof leaking, was it day or night, and were they drinking their water from clay cups?