I have been reviewing your demos here and believe I have found an error/typo: http://demos.kendoui.com/dataviz/api/index.html
Under Configuration > series > type="line" you have a "stacked" property that can be set. However, when I set this property to true my series do not stack. I noticed that under "View Code" that instead of a "stacked" property, a "stack" property is used. I changed my code to use "stack" instead of "stacked" and the series now stack as expected. Is this a typo under Configuration > series > type="line"?