Add printable column not working for grouped columns

Hi all,

I am adding printable columns to the excel export using this notation:
customerTable.addPrintable("surnames", EntityListPrintable.create("surnames"));
where EntityListPrintable implements Table.Printable and getValue delivers the content of the column.
This works fine as long as I don’t use that column for grouping. When debugging, I can see that getValue does not get called on export. Do I need to configure something else for that?