Boxplot legend not displayed properly

I would like to add a legend to my boxplot which represents four different variables: A, B, C, and D. When I am running the line for legend only the symbol for the last 'D' variable appears in the legend, for the rest variables I do not have any symbol, only their description: A, B, and C. Is there something whong in my code, attached below? Thanks in advance for help.

hLegend = legend(findall(gca,'Tag','Box'),'Location','southeast', {'A','B','C','D'});