Ok, you've answered my question. The strict definition of...

Ok, you've answered my question. The strict definition of working capital is current assets less current liabilities. As such, this will include any cash. As the cash position will change with investing and financing activities, the cash position can, and normally does, change quite regardless of normal operations.

This is apart from the issue of wether or not interest expenses/income being included in the financing cashflows rather than operating cashflows.

By only including inventories, trade payables and trade receivables, you've avoided this problem.

That's pretty much what I do too.