Description:
------------
Maybe I'm misunderstanding the purpose of this function, but it's producing strange and counter-intuitive results, and it's definitely inconsistent with the Imagick function of the same name. 

Here's a version of the reproduce code that uses Imagick::cropThumbnailImage(). It corresponds to what I put in "Actual results", since it behaves as I would expect from the description.
<?
if (!file_exists('php.gif')) {
    file_put_contents('php.gif', file_get_contents('http://www.php.net/images/php.gif'));
}

$image = new Imagick('php.gif');
echo "Width: {$image->getImageWidth()}, height: {$image->getImageHeight()}\n";

$thumb = $image->clone();
$thumb->cropThumbnailImage(50, 50);
echo "Thumbnail width: {$thumb->getImageWidth()}, height: {$thumb->getImageHeight()}\n";
$thumb->writeImage('php_thumbi.gif');


Reproduce code:
---------------
<?
if (!file_exists('php.gif')) {
    file_put_contents('php.gif', file_get_contents('http://www.php.net/images/php.gif'));
}

$image = new Gmagick('php.gif');
echo "Width: {$image->getImageWidth()}, height: {$image->getImageHeight()}\n";

$thumb = $image->cropThumbnailImage(50, 50);
echo "Thumbnail width: {$thumb->getImageWidth()}, height: {$thumb->getImageHeight()}\n";
$thumb->write('php_thumb.gif');

Expected result:
----------------
EXPECTED OUTPUT:
Width: 120, height: 67
Thumbnail width: 50, height: 50

EXPECTED IMAGE:
http://img29.imageshack.us/img29/6033/phpthumbi.gif


Actual result:
--------------
ACTUAL OUTPUT:
Width: 120, height: 67
Thumbnail width: 31, height: 50

ACTUAL IMAGE:
http://img251.imageshack.us/img251/2497/phpthumb.gif