<?php
  ereg( "([0-9]{1,2})[^0-9]([0-9]{2,4})", "1/05", $regs );
  if ( ($regs[2] <= 50) && ($regs[2] >= 0) )
    $regs[2] += 2000;
  echo "Year: $regs[2]<br>";
?>

The script is meant to return:
Year: 2005<br>

However, it returns:
Year: 2505<br>

Bizzaaaarrrrrreeee! :)

It only seems to happen if the array is assigned with ereg.  A way to get around it is:
$regs[2] = (int)$regs[2] + 2000;
this then returns the correct result.

This error occured on a just-compiled php from the command line with the following configure options:
./configure --with-mod_charset=no --with-gd=no --with-mysql --enable-magic-quotes=yes --disable-debug

Finis!