Preserving Chart Formatting - Powerpivot

Help--I've been learning Powerpivot on the fly, and have created a lovely dashboard. The problem is that when I refresh the data, and/or when I change views via slicers, the chart type (which is a combo chart) reverts back to a plain bar chart. I've tried googling a solution, but haven't found anything yet that works. I've ticked off all the options boxes suggested in various google solutions. One google solution I didn't try was to build the chart from formula references to the table--I'm not sure if I can do that in Powerpivot? I did save a copy of a chart in the format I wanted as a template, but I couldn't figure out how to invoke it. There must be a way to do this so that my end users aren't boondoggled by constantly broken charts. Anyone have any tips?!

Unfortunately, I cannot upload the workbook because it contains client confidential information. But I have grabbed a few screen shots to show you what I'm talking about.
Here are the charts as I would like them to appear.
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And here are the charts when I refresh the data - they all default to bars, and my lines for the cumulative totals disappear.

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I have tried un-ticking the box for auto-formatting, both on each chart itself, and also on the options tab for the workbook, but that didn't do the trick.
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I hope these visuals give you a better idea of what I'm trying to address.

Thanks!