credit score decrease

A few weeks ago a mortgage broker ran my credit report and said it was around 805. I decided to go with my bank and today the mortgage guy at the bank told me my score is now is 789 which is surprising since it's too big of a decrease. The mortgage guy said that he see in his system that the broker last month actually somehow ran my score two times and with another run today, for a total of 3 times, that may have decreaased the score. But is that really possible? almost 20 points seems a bit high. Is this something to worry about? The mortgage guy said it won't affect my interest rate since the score is still good. But it still is a bit odd. Thanks for any input!