Gradebook: Sum aggregation is incorrect for excluded

If I wanted to exclude or drop a grade in a sum aggregated category, the value for the category changes, but not its grademax, which in turn affects the student's overall course grade. For example, I have a Tests category whose aggregation is Sum. I will first say that Tests is a subcategory to the course category, whose has an aggregation of weighted mean. Tests has an aggregationcoef of 1. Tests have three grade items whose max values are the default 100. For simplicity's sake, I made all the grades 100, but then I wanted to exclude one grade. Category's range is still 0-300, but the student's grade in that category is the correct 200. The same issue can be replicated if I dropped the lowest grade or kept the highest two.

If my written description doesn't make sense, I attached three screenshots of the issue in question:
sum_agg_bug_1.png displays the gradebook acting normally (with no drops or excludes applied to grades)
sum_agg_bug_excluded.png displays the gradebook acting strangely on an excluded grade (notice the course grade for that student changes)
sum_agg_bug_drop.png displays the gradebook acting strangely when dropping grades (the student's overall grade also changes)