I'm not sure what versions this also occurs in but the output of chunk_split() in PHP 5.0.4 does not match the output in other versions of PHP.
In all versions of PHP I have used, apart from 5.0.4 chunk_split() adds the separator (\r\n) to the end of the string. But in PHP 5.0.4 this does not happen. This had a fairly serious impact on a library I maintain so it may also affect others who are not aware of this.