When too many series are displayed, it is not possible to scroll up the legend once scrolled down

If a chart is shown with too many series, the legend of the chart is paginated. The lateral arrays let you scroll up and down the pages. Once the second page is shown, it is not possible to display the first page.

See it with the following dataset:
http://fenixrepo.fao.org/cstat/mdg/analysis.html
uid: PRIX DES PPN DU 1er TRIMESTRE DE L'ANNEE 2013 PAR REGION
