PHP function parameter call by reference--interesting 'feature'?

Running PHP 5.1 on an Apache 2.2.6 (localhost with appropriate DB permissions) on a windows XP home machine (my laptop). Function foo(in the snippet) is an implementation of an abstract object from a child object. Function get_query_resource() returns a query resource.
The expected result of the attached code snippet, for a resource with five rows, should be

Bar calls foo.
Now in foo.
Query resource rows: 5
Processing query_resource row
Processing query_resource row
Processing query_resource row
Processing query_resource row
Processing query_resource row
Foo completed successfully.

But what I'm actually getting is

Bar calls foo.
Now in foo.
Query resource rows: 5
Foo completed successfully.

The code in the while loop isn't executing.

However, if I don't pass the query resource in bar (ie, if(foo())...) then bar gets the query resource and finishes normally. Why is this?

function foo(&$query_resource=NULL){
      echo "Now in foo<BR>";
      if(is_null($query_resource)) $query_resource = get_query_resource();
      if(!$query_resource) exit("SQL error");
      echo "Query resource rows: ".mysql_num_rows($query_resource);   
      while($row = mysql_fetch_assoc($query_resource)){
           echo "Processing query_resource row<BR>";
      }
      return true;
}
function bar(&$q_r=NULL){
      echo "Bar calls foo.<BR>";
      if(foo($q_r)) echo "Foo completed successfully.<BR>";
}
 
bar();

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