Hi Joel,
The extra html from elements in tiles-def with blank values is resolved in the latest JRebel release. Can you try updating?
To give a bit more insight, the blank values in tiles-def resolve to the value “/”. When trying to insert a template it will do a request on that path and return the content. If the path returns an error code, the content will be empty.
The problem arises because of a bug in previous JRebel releases which did not respect the FileServlet settings. So instead of getting 403 from accessing your application context root, it would display a directory listing instead. The resulting html was displayed in place of the blank definition.