In this graph the column bar shouldn't be higher than 15K on the Y axis because the sum of stacked columns adds up to only 13.2K. The Y axis is higher because it adds up all the numbers in the stacked columns, ignoring the minus sign.
You can see the difference in the two screenshots below. When you add a grouping in the legend, the column chart will reflect the values corresponding to the grouping, this time the sum is the sum of the values, but the graph is to reflect the positive and negative values. But when you remove the grouping, it is reflected in the graph as a sum, so the graph can be consistent with the scale on the left.