I found out I was overpaying my mortgage company

I recently got a letter in the mail from Wells Fargo letting me know I have too much money in my escrow account and they sent me a refund. I was really surprised and somewhat upset to find out that they were holding my money. It was nice to get the $2,6752.11 check. They were also able to adjust my monthly mortgage bill so that I'll be paying $100 less a month. Has this ever happened to anyone else? It seems very strange to me.