I am closing this item as it seems to work fine for me, and there haven't been further reports of erroneous behavior. If you continue to experience the issue, please post here a runnable snippet that showcases the problem so I can investigate.

The data properties of the chart have types (IEnumerable for the series data, object[] for the axis data, but that will probably change to an IEnumerable as well in the foreseeable future). Thus, you can provide even methods that work with the data you have and return the appropriate types. If this does not work for you, could you post a simple proof of concept that shows the problem you are facing?