the following script will print out
unset
set
the first time it is run although it should actually print 'set' twice; somehow, the variable needs to be globalized again after the session has been registered.

normal php4 setup with everything compiled-in.
php -v >> 4.0.6devel
---------------------
function test()
{
  global $glb_var;

  session_save_path("e:\\temp");
  session_start();
  session_register('glb_var');

  test2();

  print "glb_var='$glb_var'<br>";

  global $glb_var;
  print "glb_var='$glb_var'";
}

function test2()
{
  global $glb_var;

  $glb_var = 'set';
}

$glb_var = 'unset';
test();