Apart from resolution there is also the aspect ratio. Even if you use the stretch mode Remote Utilities honors the aspect ratio so that your remote screen, albeit stretched (or shrunk) still shows correct proportions without distortion.
You will not see the black bars only if the aspect ratio of your local computer is the same as the aspect ratio of the remote one, although their resolutions may differ. If the local resolution is higher than the remote one - stretching occurs. If the remote resolution is higher than the local one, shrinking occurs.
By zip file you mean this one, the main "package" on the download page, correct? This is in fact just Viewer and Host zipped in a single file for convenience. You can as well download them separately below on the page.
Anyway, we'll take a look and contact Symantec regarding this issue.