Terry, I would believe that the lease should also set out what may happen with the security bond, should the tenant go into liquidation or administration. The landlord needs to mitigate their loss, which I see that they have done in this situation. I bow to your knowledge of "equitable lease" or interest, however in Qld the property law act requires an agreement to be in writing to enforceable. That to me suggests that the current situation is a verbal tenancy, and the landlord has options.
The problem here is that the tenant has ceased to exist a while back but the landlord has continued to lease the property to a third party as if the lease were in place. The landlord would therefore have an equitable lease with the people who are in there and paying the rent.
Sounds like the landlord wants to keep the tenants, so this lease should be put into legal form and perhaps the terms renegotiated.
There are also issues with the insolvency of the previous tenant which could effect the landlord. e.g. the security bond. Care must be take when considering handing this back as if you give it to the current tenants the liquidators of the company could cause you to pay it again to themselves as the previous company was the owner of that bond.