When typing out a URL in a checklist item, two spaces are required to create one space in between the URL and any text before it.
I.e. "Create thumbnail and test with http://thumbsup.tv" requires two spaces after "with" to render a space between that word and the URL.
Side note - would be awesome if we could turn text within checklists into hyperlinks! The checklist I'm building will be a template on every video task, so hyperlinking would make it look cleaner.