Now, it is time to look back at merit chronological history.
One year anniversary of merit systemIn short, what you discussed is here:
3) Second adjustment: Enhanced newbie restrictions & requirementsDue to excessive garbage-posting, you now need 1 merit to be a Jr Member. All existing Jr Members who didn't meet the requirement were demoted. Also, newbies can no longer set any signature or personal text.
Let me clarify that demotion on Junior Members whom have not earn a single merit (at least) means that they will become Newbie, and their signature automatically disabled by forum system.
To sum up, that case OP raised is likely a glitch.