Price in Sales Order is different between Lines tab and Totals tab in Sales Order

We created a Sales Order with a large number of line items.  The Total Amount shown on the bottom of the window is correct.  When we then navigate to the Totals tab, the Taxable Amount is a completely different number - inflated by almost $30k.  We sent this quote to our customer not noticing the discrepency.  

Any idea why this is happening?  This is the only instance we have noticed so far: