Well, thing is hostnames are supposed to only contain letters, digits and hyphens, although other DNS names can contain underscores. So it shouldn't work. You should be able to have a TEXT record with an underscore, but really shouldn't be able to have an A or AAAA record.
In this case optimus_prime is a sub domain. The actual DNS entry is likely *.jpg.to so DNS does not have to know how to resolve the URI section with underscore.
