I have 3 line items in a sales order, all are the same non-inventory taxable Item.  The first was the original Sales Order amount (over $1million), the second was a minor addition to the sales order, and the third entry was a credit for an amount removed from the original order.  
 
When I go to release the lines, the first line shows taxable Y but no tax is calculated.  When I release the second and third lines, tax is calculated.  Since the third entry is a credit, I end up with the pre-tax sales order as the subtotal and a negative sales tax.
 
Any ideas on why DBA won't calculate the correct sales tax?
 
Thanks in advance for any help.

I tried breaking the first line into two pieces, both under $1 million, but that didn't make any difference.

All 3 Items are Item Number "OTHERS", a Type N, non-inventory item.  IN-B is set to taxable Y, AR-A for the customer is set to taxable Y.  I've deleted and re-entered these lines several times trying to get this to work.  I have had various results, including sometimes getting the tax calculated on the second and third entries of the Item, and other times getting no tax calculated whatsoever.
 
I will try some other variations to see if there is a field width limitation on the taxable amount and also on whether there is a field width limitation on the sales tax amount.  If  anyone has any other suggestions, I would appreciate hearing them.

This is really bizarre.  
I changed the price of the first item so that the sales tax would be 99,999.99.  It printed correctly on the Acknowledgment, SO-E screen, and the Invoice.  
I added $0.50 to the price to make the sales price exceed 99,999.99 and it printed correctly on the Acknowledgement, but the SO-E screen showed a 0.00 tax amount when that line item was released, but when I printed the invoice, it was correct.  
Finally, I went back to the original price on the first item.  The Acknowledgement printed correctly, the SO-E screen showed a zero tax amount on that item and showed an incorrect total tax and total amount.  When I printed the Invoice, however, it didn't even show a line for sales tax!  There is no logic to this.