The problem with php as apache module.

<directory /document-root>
  php3_engine off
</directory>

<directory /document-root/php-enabled>
  php3_engine on
</directory>

Seems does not work. I've tested compiled with a
debugger and found, that in mod_php3.c in function
php3_merge_dir merge is done by the way:

  memcpy(new, base,...);
  if(orig->x != add->x) new->x = add->x;

And new is just copy of the base. So, apache
per-directory (location) configuration does not
work as desired. That code seems to be in php-3.0.11
too.