In a recent ticket it was found that repository validation no longer allowed % characters.
When trying to enter one (e.g. "http://www.bower.org/space%20init") , the validation reads "URL should be in the format 'http://www.example.com'".
This is too generic to be helpful here. If we're going to restrict things, it should be a similar makeup to ID (e.g. "Only letters, digits, underscores(_), hyphens, and dots(.) are allowed and may not start with underscore or dot." so people don't have to guess).
From nexus.log as well: