Excel 2007+ files with Graphs defined as worksheets cannot be opened

[lorenzulrich]

Graphs in Excel files can be moved to an own worksheet, that - contrary to "real" worksheets - cannot contain any data but are just a "full worksheet" representation of a Graph.

(Right click a Graph --> click "move graph" --> select "new worksheet" option)

Such files (or at least the special Graph worksheets mentioned) cannot be read in PHPExcel; the following error is thrown:
"#1: Notice: Undefined index: rId4 in /var/www/typo3.flow/Packages/Libraries/phpoffice/phpexcel/Classes/PHPExcel/Reader/Excel2007.php line 651"