None of our released versions have exhibited this behavior and I can not repro the issue from your current description.
Could you provide more details (IIS version, browser type/version, C1 version, perhaps other steps repro that are relevant)? You can find version information in the "Help | About" menus - please specify full version number.
Are the images you insert from "manual URL's" placed outside the C1 media archive or did you insert them from the archive?
Could you send an example of the image URL before/after?