After filter return a null model when rendering templates

The model attribute of the after filter is set to null when a render template is called instead of returning a model.

In the attached sample project, I have a filter that simply prints out the result:

after = { model ->
     println model
}

When I do a standard view render, it returns a correct model.

def good = {
     [ test: 'test' ] 
}

call http://localhost:8080/filterBroken/broken/good

Output: [test:test]

However, when I call a template render, it returns null instead of the expected [test:test] model.

def bad = {
     render( template:'/bad', model:[ test:'test' ] )
}

call http://localhost:8080/filterBroken/broken/bad

Output: null
Expected: [test:test]