ActiveRecord `readonly? = true` is preventing `destroy`
<p>According to all the documentation and tutorials I've found, defining the following method in my ActiveRecord subclass (<code>AuthenticationToken</code>) should prevent saving changes to an existing record, but not prevent it from being created or destroyed:</p>

<pre><code>def readonly?
    !new_record?
end
</code></pre>

<p>However, calling <code>token.destroy</code> throws <code>"AuthenticationToken is marked as readonly"</code>. For now I am using <code>token.delete</code>, which is acceptable because the model has no children, but I'd like to be able to use destroy. I'm using Rails 4.2.5.</p>