The same effect occurs for the imageellipse(), I belive this bug is in libgd

Please try using this CVS snapshot:

  http://snaps.php.net/php5.2-latest.tar.gz
 
For Windows:

  http://windows.php.net/snapshots/

No feedback was provided for this bug for over a week, so it is
being suspended automatically. If you are able to provide the
information that was originally requested, please do so and change
the status of the bug back to "Open".

I can confirm this still occurs in PPH 5.2.9-1

An elipse with an even size is rounded to an odd size

Reproduced error on the following:

* PHP Version 5.2.5
* GD Library bundled (2.0.34 compatible) 
** IIS 5.1 on Windows XP Professional
** Apache/2.2.9 (Win32) on Windows XP Professional

Reproduce code:

<?php
  $radius = 100;

  $corner_image = imagecreatetruecolor(
    $radius * 2,
    $radius * 2
  );

  $clear_colour = imagecolorallocate(
    $corner_image,
    0,
    0,
    0
  );

  $solid_colour = imagecolorallocate(
    $corner_image,
    0xFF,
    0,
    0
  );

  imagefill(
    $corner_image,
    0,
    0,
    $solid_colour
  );

  imagefilledellipse(
    $corner_image,
    $radius,
    $radius,
    $radius * 2,
    $radius * 2,
    $clear_colour
  );

  header( "Content-type: image/png" );
  imagepng( $corner_image );
?>

Expected output:
* 200x200 black circle inside 200x200 red square, perfect fit

Actual output:
* 201x201 black circle inside 200x200 red square, the right side of circle clearly appears "clipped"

Read the last line of the previous comment as follows:

* 201x201 black circle inside 200x200 red square, the right and bottom sides of the circle appear "clipped" by one pixel

Here is the output from the above script.

radius = 100px, canvas size = 200x200px
http://img235.imageshack.us/img235/9236/radius100canvas200.png

radius = 100px, canvas size = 201x201px
http://img235.imageshack.us/img235/3249/radius100canvas201.png

I believe there is enough feedback on this and the bug should be re-opened.