Computing return value with typed closure parameter does not properly work for Object... methods

I stub a method that takes Object... as parameter, which is called addEventListener.
I wanted to perform some side-effects on the parameter, so I wanted to do this with a typed return value closure as usual like

1 * jda.addEventListener(_) >> { Object[] listener ->
    listener.each {
        it.doSideEffect()
    }
}

Unfortunately this does not work as I'm used to.
When the parameter is untyped I get

• the listeners
• in an object array (as given to the method)
• in an array list

With the Object[] typed parameter I suddenly get one level more instead of less

• the listeners
• in an object array (as given to the method)
• in an array list
• in an object array

Start by reproducing the addEventListener stub with the typed Object[] closure parameter shown in the issue, then compare it with the untyped closure behavior. Trace how typed closure arguments are computed for Object... methods; done means the typed form receives the expected listener values without the extra Object[] nesting.