Created attachment 136654 [details]
sheet with pivot table and pivot chart

The current solution of pivot charts uses e.g the structure
<table:table-cell office:value-type="float" office:value="NaN">
    <text:p>NaN</text:p>
    <draw:g>
        <svg:desc>PT@data 0</svg:desc>
    </draw:g>
</table:table-cell>

to define an identifier for the cell, that will be used in a cell reference.

This structure gives no formal error, but I will surely not support the idea of miss-using a description of a graphical element as identifier for a table-cell.

There exists more suitable solutions.
Currently possible is
attribute xml:id
or
as part of the entire table the element
<table:named-expressions> with its child element <table:named-range>.

This problem should be solved together with bug 112783.