Non-Operating working capital is due to the Timing differences between purchase and payment for Capital expenditures, for non-Recurrent items, etc. In practice, non-Operating working capital is a catch-all category for items that cannot be classified anywhere else. It includes amounts due on Fixed assets, dividends to be paid, Extraordinary items, etc.

(See Chapter 4 Capital employed and invested capital of the Vernimmen)

To know more about it, look at what we have already written on this subject