Archive Credentials Must be Entered Twice: First Try Always Fails, Second Always Succeeds

Using ABR10 Workstation 13544 on Win7x64.

When I click to edit a backup plan, the configuration screen reports that it cannot obtain the Archive location information because it cannot get access to the location. When I click on the "Provide Access Credentials" link, I get the usual dialog box asking for username and password.

I enter the domain credentials for the Archive location. This invariably fails. I repeat the process, and enter the exact same credentials again. This invariably works, and thereafter I can edit the backup job.

This happens on several workstations, so it's not specific to a particular machine.

What's going on here?