A/R invoice was closed even there are open balance

Hi,

I had a situation here.

An invoice with amount due of US 1,000.

Create an incoming payment  > payment mean > cash paid US 600,

The incoming payment indicate an open balance of US -400.

However, when I check back the invoice, the status is closed and the applied amount is US 1,000, the balance due is 0.

Isn't the balance due should be 400?

I cannot find the invoice in the incoming payments anymore

Thanks