More details on this would help.
One factor to look at: Your summary fields compute values drawing from all the records in the current found set. If you change the found set, you will change the results of any calculations that refer to them.
These fields are tracking donations and do change monthly. Does this shed enough light on my conundrum?
Spell out the field definitions.
Any relationships involved or are all the fields being used part of the same table?
What happens to the displayed values of these calculations when you close/reopen the file?
Are you always examining these values with the same exact found set or might reopening the file change the found set to give you a different result from what you expect?
Thanks your last question was where I blew it. Its now accurate.