debugging PHP memory corruption

We've got a problem with PHP 5.3.8 and a third party (open source)
library (WSo2 SOAP).

At some point during the request to the PHP script, some structures seem
to be getting corrupted causing PHP to crash.

Depending on the code in the PHP script, it's either crashing during in
a print_r/var_export or crashing when the PHP shuts down (the exact
location of the crash moves around when we alter the code).

We can reprod this on Win32 and Linux now. But how can we go about
debugging where the corruption occurred? The address of the corrupted
data is not known until the segfault/access violation occurs so we can't
set a watch on it (as far as we can tell).

Here's what we see in the debugger on Win32:

Unhandled exception at 0x1008eb45 (php5ts.dll) in php-cgi.exe:

Access violation reading location 0x4cac5400

php5ts.dll!_zval_ptr_dtor(_zval_struct * * zval_ptr=0x4cab5400) + 0x5
bytes

php5ts.dll!zend_hash_destroy(_hashtable * ht=0x034cc0f0) + 0x27 bytes

php5ts.dll!zend_objects_free_object_storage(_zend_object *
object=0x03489fa0, void * * * tsrm_ls=0x003f42b0) + 0x2b bytes

php5ts.dll!zend_objects_store_free_object_storage(_zend_objects_store *
objects=0x003f685c, void * * * tsrm_ls=0x003f42b0) + 0x9c bytes

php5ts.dll!shutdown_executor(void * * * tsrm_ls=0x003f42b0) + 0x2fe
bytes

php5ts.dll!zend_deactivate(void * * * tsrm_ls=0x003f42b0) + 0x91 bytes

php5ts.dll!php_request_shutdown(void * dummy=0x00000000) + 0x31f bytes

php-cgi.exe!main(int argc=1, char * * argv=0x003f31d0) + 0xe89 bytes

php-cgi.exe!__tmainCRTStartup() + 0x10f bytes

Any tips welcomed.

Andy.

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