I have the same problem. I have a stacked bar chart with sales by year (each bar has different sales categories) and a treemap with customers. If a customer is selected in the treemap, this customers share of the sales is higlighted in the bar chart. In some cases it can happen that a customer has a negative value for the sales, altough the total amount is positive. If this happens the bar chart is filtered instead of highlighted (since you can't higlight a negative value in a positive total). The filtering is indeed confusing for the end user. Keeping the highlighting would off course mean that the highlighted part goes outside of the total, so maybe change the thickness of the highlighted bar in this case? This way you can still see how the selected part compares to the total.