Zend Engine question

Are there any tools for debugging ZE? I've got a problem with huge script that at some point behave like all variables were reference to single variable. I suspect that there is something wrong with EG(uninitialized_zval). Any hints how to fight it? I've compiled it with ZEND_INTENSIVE_DEBUGGING and it found nothing. When I debug it with simple debugger I can see that all ZEND_FETCH_W opcodes receives the same zval address and ZEND_ASSIGN doesn't change it. I don't know how it should work yet, but I'll learn it soon. Maybe someone could give me a piece of advice? Regards, Wojtek