Tab lock does not prevent the tab from closing. The different tab lock modes and what they do are documented here: Basic Concepts / The Lister / Tabs.
A fairly simply script which uses the OnCloseTab event and Tab.lock property could prevent locked tabs from being closed, if you want to extend the meaning of tab locking to do that.
Re post editing, see my reply here which you seem to have overlooked: Re: Activated pro trial, now dopus opens in 2 applications each time and there is no way to only use one that I can find.