I have a serial chart with a field that splits that chart by project phase, giving me a stacked bar chart with up to 6 phases/colors. However, most projects only have 1 phase (Construction). The chart legend appears as expected if I filter the chart to a project that has 2 or more phases.

However, filtering by a project that has only a single phase causes the legend to disappear and makes it confusing for users to know which phase the bar chart is displaying.

Is this a bug or is this how the tool is supposed to work?