Background Transfer without prompt for key passphrase?

The SSH2 server use public/private key for authentication. And on connection, WinSCP will prompt for passphrase of private key.

The problem about background transfer is: When network error occurs, it prompts for key passphrase for re-connect and resume. How to turn off that?

We upload large video files to server over the night, and no prompt needed.

WinSCP 4.1.8, and the 4 checkboxes for "Background transfer" all checked including:
No confirmations for background transfers;
Remember password of main session for background transfers.

Many thanks.

The checkbox "Remember password of main session for background transfers" on the transfers->background tab doesn't seem to work for the first transfer. In fact it has never worked for the first transfer as far as I recall. Each download queue you have requires that you re-enter the name and password (for tunnels it's even worse, you have to enter both tunnel and session passwords). It is only when you start the queue the first time, after that, each queue seems to remember its password, but it still means you have to enter the tunnel and system passwords many times:

First when initially logging into the server. Then once for each transfer queue you set up. And if a connection is lost (for example after loosing wireless connectivity and regaining it), you need to re-enter the password a third time for every queue you have active.

The expected behaviour for me when "Remember password..." is checked would be: I only ever enter the tunnel and system password once, when first logging into a system. Then, as long as that session is active I never need to enter the passwords again. If I get unexpectedly disconnected I get automatically reconnected (including full login, going through the tunnel, etc) and operations resume without me intervening or entering passwords again.