I've noticed an odd problem with site rules. I use Chrome and have always had problems with DS properly and consistently intercepting and reacting to clicks on downloadable file links. That's not the issue at hand; I mention it only to provide context for what follows. A more reliable approach has proven to be right clicking on a link and then selecting "Download Link" from the context menu. Here's where the problem arises.

The first time I do the "Download Link" thing on a site, DS pops up a window asking for username and password for the site in question, despite there being a site rule to provide that information. If instead I "Copy link address" and manually add the download to DS, the file downloads without any further intervention on my part. Having done this, subsequent "Download Link" actions also work without prompting for username and password. Manually adding the first download appears to prime the pump for "Download Link".