It sounds like it may be throwing a Dojo error, possibly something to do with IDs. I don't think this widget will solve that problem - it's an extension of the core Dojox class to give the option to make it multi-column.
I have an XPage with multiple charts, each with a legend on it. That's working, but I'm using a custom control for the chart, passing in the data for the chart put also a numeric variable (e.g. 1, 2, 3). Instead of using:
var chart = new dojox.charting.Chart2D(“#{id:simplechart}“);
chart.setTheme(dojox.charting.themes.PlotKit.orange);
I then use:
var chart#{javascript:passedKey} = new dojox.charting.Chart2D(“#{id:simplechart}“);
chart#{javascript:passedKey}.setTheme(dojox.charting.themes.PlotKit.orange);
So wherever I'm using a JavaScript variable to refer to the chart, I'm using a different variable for each chart. That works for a single XPage with multiple charts each with its own legend. Not sure if that will solve youor problem too. (Alternatively, it might be throwing a Dojo error to the Firebug console which may help identify the cause.)