99% of the time a URL is added to the disambiguation (aka comment) field, it is done incorrectly. The problem occurs quite often, in particular for labels added from within the release editor. In that particular case, the long-term solution would probably involve redesigning the "Add Missing Entities" tab to include a more complete Add Label form.

As a way of handling the general problem, I propose disallowing the addition of URLs to ALL disambiguation fields; instead, we should prompt the user with a helpful comment, which could even re-use existing text ("The disambiguation field is used to help users distinguish between identically named entities. It is not a place to store URLs related to the entity: that kind of information should be either added using the appropriate relationship, if available, or stored in the annotation field.").