Can't export custom fields into cvs

As it turns out, it is impossible to export contact data of non primary fields as cvs.
I have tried to export a search and use custom fields in it. I can select al the fields I need, and even save them as custom field selection. But if I export it, the columns in the actual cvs file are titled: "custom_1, custom_2,..." and no field data they are absolutely empty, only the selected primary fields are saved correctly.