
ANSWER:You are correct that it is prohibited for the solo 401k owner to purchase a property that has ever been owned by him or her. This would be in violation of the following rule.
Sale, exchange, or leasing of property between a plan and a disqualified person;
See following links for more information.
http://www.mysolo401k.net/self-directed-401k-prohibited-transaction-4975/
http://www.mysolo401k.net/prohibited-transactions-solo-401k/