Sales by Customer reports

Hi

I have run a report (sales by customer summary) on accrual basis, and would have expected this to show totals for all sales invoices raised, by customer, ie a Top Customer report if you like. 

It does, but I have a line which is "Not Specified".  When I drill down, this is showing other income, like bank interest received, a VAT refund we had, and our £10K business rates grant paid to us.  

Is this normal?

Thanks.