Problem

When there are certain custom fields defined there is an issue with "Export metadata" click - it causes PHP exception thrown.

The exception is caused when array is passed as $value in the following line of application/modules/editor/Models/Task/Excel/Metadata.php file (addTask function):

$sheet->setCellValue($sheetCol . $this->taskRow, $value);

Sample taskColumns:   Array (
    [0] => id
    [1] => state
    [2] => userState
    [3] => userAssocDeadline
..
    [25] => enableSourceEditing
    [26] => customField4
    [27] => customField2
    [28] => customField1 )

$value causing the reported issue:
customField1
Array
(   [en] => first value dropdown
    [de] => erster Wert Dropdown )

Solution

Temp. solution was to exclude such fields from the export with a need for a better implementation.