Getting wrong result from subtraction calcuation

I'm getting the wrong result from a simple subtraction calculation. Thinking that I might need to aggregate the calculated fields, I wrapped each field in a sum, but the result is still wrong. 3,808-3,426 should be 382 (rather than 377).

Here's the calc:

Difference in Number of Gifts YTD, Current to Prior Year

SUM([Number of Gifts YTD Current Year])-SUM([Number of Gifts YTD Prior Year])

Here's the result:

I would greatly appreciate any suggestions! Workbook attached.