Unrealized Sales Tax

We have scenarios where customers will pay before they are invoiced. Our customers are set up with Application Method = Apply to Oldest (automatic application of payments). We have Unrealized Tax set up on the GL setup. We also have Unrealized Tax Type set to Last (Fully Paid) in Sales Tax Juristiction setup. When an invoice is posted which automatically applies it to the prepayment, the tax is posted as unrealized. It never moves to the amount field in the VAT Entry Table (i.e., is never realized). Does anyone know how to make this work without using Application Method = Manual?