Please add support for named stacks in Area and Line charts. It should work similar to Bar/Column charts. For example, with the following series definition [{field: 'Whole', stack:'whole', name: 'Whole Part'}, {field:'Part1', stack:'parts', name:'Part 1'}, {field:'Part2', stack:'parts', name:'Part 2'}] Part1 and Part2 should stack but not "Whole".
What do you mean by stacked separately for area chart in this case? Can you show a mockup/visual which illustrates what you have in mind?
Simple stacking works as expected. However, as you can see in your demo, there is no difference in the behavior whether stacks are named or simply flagged as "true". In your example stacks "webkit" and "other" are not stacked separately.
I think this is supported now. If you try this quick demo: http://dojo.telerik.com/AqIcU you should not be able to see the Safari series item stacked in the area chart visualization. Let me know if I am missing something obvious.