The themes for new users is always set to "default" when a new account is created. Since the "Anonymous" user account is used when a user is not logged in, or doesn't have an account. you would think that a new account would adopt...
The CommunityServer.Components.HtmlScrubber is removing spaces from "src" and "href" attributes, which it shouldn't be doing. If you use the "basic blue" theme, or any other theme that has a space in it, images may not...