Unable to get strpos() to work correctly in class method

I have written a class with a method that uses the strpos() function, but I can't get it to work. However, when I use the method as a function in a simple test program that uses the identical code to simulate the class method (and feed it the same strings) it works exactly like I expect. Below is an abbreviated version of the non-working method version. However, both versions are identical to this point, only this doesn't work while the test program version does. The problem is that the while-loop never executes because $start always comes up false (but only in the class version).

protected function extract_quotes($string) // Assumes if $string has quotes they are an even number of them // Uses class property $keywrd_frags to store parsed fragments {

    $delm = chr(34); // quote char in this case
    // start parsing from first character of incoming query string
    $start = strpos($string, $delm, 0);  //<=== POINT OF FAILURE
    while($start !== FALSE)
    {
    	  // the while loop extracts all the delimited blocks of text
    	  // one at a time until there are  none left.  At that point
    	  // $start will be false and $string will have only

// un-delimited text (or an empty string)

     	     //This section never runs because $start is always FALSE

    }
        // No more delimited text, so return the remaining $string
    return $string;

}

What am I overlooking in the class version that keeps the code from working there? Tried: I've tried 37 dozen different variations on this theme, including dropping the $delim variable and using '"' in the strpos() function. I've also used different delimiters, and even changed the delimiter character once the string got into the extract_quotes() function. No difference. Running:

Apache Version :    2.2.17
PHP Version :    5.3.3

Thanks for any ideas, Jonathan