<?php
   $in = "<pfw:image name=\042novedad\042/>";
   $out = pfw_f1($in);
   $out = pfw_f1($in);
   ...
   $out = pfw_f1($in);
   echo "out: _", $out, "_";
?>
------------
If only few 'pfw_f1($1)' calls, nothing rare occurs; but if you put "a ton" of these calls: then become that error. The 'pfw_f1()' function is not "memory hungry" nor "memory allocation buggy" (tested). I think that zend/php syntax analyzer may have a limit for token labels (parser fault?). Well, I'm not sure.

-------------
configured as: ./configure  
               ./configure --enable-pfw
----------
php.ini: no manually touched nor intentionally changed
-----------
Console data dump:

]$ php t0
X-Powered-By: PHP/4.0.0
Content-type: text/html

<br>
<b>Fatal error</b>:  Call to undefined function:  pfw_f1() in <b>t0</b> on line <b>
5</b><br>
]$ ls -la