You'll now see the credit limit warning (and preventing confirming/dispatching orders if configured) when the customer is either over their credit limit or has overdue invoices. Prior to now, this warning was only shown if the customer had actually exceeded their limit, but it will now also be shown if they have unpaid overdue invoices.

Update 23rd Dec: If you'd like the old functionality back (where just the limit is checked and overdue invoices won't trigger a failure), you can untick the "Fail credit limit checks if there are overdue invoices, regardless of the credit limit amount" box in Settings > Order/invoice settings.