23 nothing is so as it seems, but why

Today during a session i had a strange "magic" feature found in php. <?php $a = 10; echo ++$a + $a++; ?> this works perfect as expected. it returns 22. but if i assign $a as a ref. to another variable it will be return 23. <? $a = 10; $b = &$a; echo ++$a + $a++; ?> this will gave me to 23 (used the $b to the pre post stuff) <? $a = 10; $b = &$a; echo ++$b + $b++; ?> this just happens if i have a ref. count to my var. WHY? :) http://en.wikipedia.org/wiki/23_%28film%29 -- Marco Kaiser