It is very simple to reproduce. Create a .html file. Link to some image inside of it. Add these to your hg repository. Link to the .html file from a Wiki page. The html will load, but the images and other resources can not be accessed because they are relatively referenced in the .html or hard coded and they don't have the token that bytebucket.org expects to be on the end. The documentation for the wiki says you can link to any file type. These same files work fine if referenced from some other web server or locally on the hard disk on the developer machine.
Issue #6219 wontfix