Customize Address with +4 Zip = Order Save Error

We've been having a problem with some users complaining about getting an "Unexpected Error" when saving orders in NetSuite.

I've figured out that the problem derives from the code behind the -Customize- Address functionality on the Sales Order/Address tab and how that code interacts with the Tax Items.

Our Tax Items our loaded with just 5 digit Zip Codes.

When customers have 9 digit (+4 Zip Code) Zip Codes, the Sales Order is able to correctly find the appropriate Tax Item to use on the Sales Order when the Sales Order is first created.  However, if a user goes into the Sales Order/Address tab and chooses to Customize the Ship To (haven't tested on Bill To yet...) Address and the final address still has a 9 digit Zip Code, the Tax field value will switch to -Non Taxable-.  If the user doesn't notice the switch and tries to save the order, he/she will get the "Unexpected Error".