Generate chart with data.x without other columns

I have this problem - when I'm trying to generate chart with data.x = "x", but not loading any columns yet (columns param has only "x" array), after I call load c3 gives me error **'x is not defined for id = "data3"'**. If I generate chart with atleast 1 column except "x" given, all works fine.
Ideally I don't want to generate chart with "x" column given too, I want to use chart.load(columns["x"...]) later and then load all other columns.
Here is fiddle to show the problem. If you uncomment data1 in generate function, all works fine, even loading new data3.
http://jsfiddle.net/missingdays/ccc0Lyk2/2/
Is there any way to fix this on my side, or this is just bug?