Iron Router: contentFor doesn't work with 'sublayouts'

Suppose a set of templates like this:

<template name="layout">
  layout<br/>
  {{> yield "title"}}
  {{> yield}}
</template>

<template name="sublayout">
  sublayout<br/>
  {{#contentFor "title"}}test{{/contentFor}}
  {{> yield}}
</template>

<template name="content">
  {{#Layout template="sublayout"}}
    content<br/>
  {{/Layout}}
</template>

With a route directed to content using layout. The contentFor helper in sublayout cannot seem to ‘find’ the title region. Is this by design, or a bug? Is there a workaround?