The example output is different on my side:<?php/*object(Threaded)#2 (11) { ["0"]=> int(0) ["1"]=> int(1) ["2"]=> int(2) ["3"]=> int(3) ["4"]=> int(4) ["5"]=> int(5) ["6"]=> int(6) ["7"]=> int(7) ["8"]=> int(8) ["9"]=> int(9) ["foo"]=> string(3) "bar"}*/?>for windows usingPHP_VERSION 5.6.11php_pthreads-2.0.10-5.6-ts-vc11-x86.zip @ http://windows.php.net/downloads/pecl/releases/pthreads/2.0.10/and linux usingPHP_VERSION 5.6.10-1~dotdeb+zts+7.3So $stdClass wont be merged.