`ensure => latest` doesn't work properly with release canditates

I have the following puppet manifests:

  class { 'php':
    ensure       => 'latest',
    manage_repos => true,
    fpm          => false,
    dev          => true,
    composer     => true,
    pear         => true,
    pear_ensure  => 'latest',
    phpunit      => true,
    extensions   => {
      # ...
      xdebug   => {
        ensure   => 'latest',
        provider => 'pecl',
        zend     => true,
      },
      # ...
    },
  }

Running puppet always causes the following output:

Notice: /Stage[main]/Php/Php::Extension[xdebug]/Package[pecl-xdebug]/ensure: ensure changed '2.3.3' to '2.4.0RC4'

Running puppet --debug shows the following:

Debug: Executing: '/usr/bin/pecl remote-info xdebug'
Debug: /Stage[main]/Php/Php::Extension[xdebug]/Package[pecl-xdebug]/ensure: pecl-xdebug "2.3.3" is installed, latest is "2.4.0RC4"
Debug: Executing: '/usr/bin/pecl upgrade xdebug'
Notice: /Stage[main]/Php/Php::Extension[xdebug]/Package[pecl-xdebug]/ensure: ensure changed '2.3.3' to '2.4.0RC4'
Debug: /Package[pecl-xdebug]: The container Php::Extension[xdebug] will propagate my refresh event

Running these commands manually:

> /usr/bin/pecl remote-info xdebug
Package details:
================
Latest      2.4.0RC4
Installed   2.3.3
Package     xdebug
License     BSD style
Category    PHP
Summary     Provides functions for function traces and
            profiling
Description The Xdebug extension helps you debugging your
            script by providing a lot of
            valuable debug information. The debug
            information that Xdebug can provide
            includes the following:

                * stack and function traces in error
            messages with:
                      o full parameter display for user
            defined functions
                      o function name, file name and line
            indications
                      o support for member functions
                * memory allocation
                * protection for infinite recursions

            Xdebug also provides:

                * profiling information for PHP scripts
                * code coverage analysis
                * capabilities to debug your scripts
            interactively with a debug client

> /usr/bin/pecl upgrade xdebug
Nothing to upgrade

Reproduce the manifests shown for the php class and the xdebug extension, then compare puppet's Package[pecl-xdebug] handling with the listed pecl remote-info and pecl upgrade output. Trace how ensure => 'latest' interprets the 2.4.0RC4 version, and define completion as consistent behavior when pecl reports that release candidate as unavailable for upgrade.