Problem using SUM() function with nested IF()

Gang, first post here on the Excel forums. I find that I can usually resolve my Excel quirks with a few Google searches... no such luck in this case. Also, I will probably provide too much info in this initial post... for a problem with a simple solution. Please forgive.

If you view the first attachment, you will see the data I am working with.

In column A, I have dates. In column B, I have weights. In column D, I have the first month I'd like to investigate. Basically, the formula below will be in cell D2 and add all of the weights from the month of January. Simple, right?

Here is the forumla:

=SUM(IF(MONTH(A2:A9)=MONTH(D1),B2:B9,0))

As you can see by the first attachment, the result as reported IN THE CELL is 0. But, if you look at the second screen shot, you will see that the function builder reports the (correct) value as 16048.

I suspect that the problem is in the sub-function MONTH(A2:A9) as A2:A9 is not a serial number argument as the function is expecting.

What causes the function builder to report a different value than is placed in the cell? Any suggestions?

Thanks in advance for the help...