With pivot tables, it's often the little things that are frustrating..doesn't show up when you refresh, number formatting goes missing, fields have weird names...things like that.
Amazingly, that you give away so much for free, but it works in terms that I am your fan now and will be recommending your site at any opportunity I have.
1 - It is best to put the charts on their own chart sheet.
Better if you create custom size chart pages in Excel so you don't have to resize the devils in PPT. worksheets is that the size information seems to be somehow embedded in the upper left hand corner of the chart.
Now, that upper left hand corner is always "visible" to the linking mechanism during update links since a chart sheet is 100% "visible".
Now a worksheet may not be 100% "visible" if you stuck the charts all over the place in a worksheet.