SUM results not matching up to summary
I'm having an issue with SUM giving me unexpected results.
When I'm working with hierarchy lists and just need a top level sum rather than subtotals at all levels of the hierarchy, sometimes I'll use a 1-item list, add a line item set to this list item, and SUM over it to get the top level sum. It's a little convoluted but saves space and calculations vs. turning on summary over all the intermediate hierarchy levels.
However, I just tried this and got a different number from the line item summary. While the line item summary gives me 276 at the top level (which is correct,) using the SUM function over my helper list item gives me 282.
I can't figure out why this is happening. Is there something I'm missing/forgetting about using SUM in this way?