This is the backtrace that suggests me it's from mysqlclient:

Program received signal SIGSEGV, Segmentation fault.
zval_mark_grey (pz=0x13539974) at /build/buildd/php5-5.3.2/Zend/zend_gc.c:356
warning: Source file is more recent than executable.
356					p = Z_ARRVAL_P(pz)->pListHead;
(gdb) bt
#0  zval_mark_grey (pz=0x13539974) at /build/buildd/php5-5.3.2/Zend/zend_gc.c:356
#1  0x08328d08 in zval_mark_grey (pz=0x13539974) at /build/buildd/php5-5.3.2/Zend/zend_gc.c:367
#2  0x0832970d in gc_collect_cycles () at /build/buildd/php5-5.3.2/Zend/zend_gc.c:417
#3  0x08329995 in gc_zval_possible_root (zv=0x13f32a8c) at /build/buildd/php5-5.3.2/Zend/zend_gc.c:166
#4  0x082fd4c1 in _zval_ptr_dtor (zval_ptr=0xbfffd16c) at /build/buildd/php5-5.3.2/Zend/zend_gc.h:183
#5  0x0835cc09 in zend_do_fcall_common_helper_SPEC (execute_data=0x13f32a8c) at /build/buildd/php5-5.3.2/Zend/zend_execute.h:316
#6  0x08333d8e in execute (op_array=0x8909d28) at /build/buildd/php5-5.3.2/Zend/zend_vm_execute.h:104
#7  0x08309fa6 in zend_execute_scripts (type=8, retval=0x0, file_count=3) at /build/buildd/php5-5.3.2/Zend/zend.c:1266
#8  0x082ae754 in php_execute_script (primary_file=0xbffff674) at /build/buildd/php5-5.3.2/main/main.c:2288
#9  0x083a0c28 in main (argc=7, argv=0xbffff7b4) at /build/buildd/php5-5.3.2/sapi/cli/php_cli.c:1196
(gdb) p op_array
No symbol "op_array" in current context.
(gdb) frame 6
#6  0x08333d8e in execute (op_array=0x8909d28) at /build/buildd/php5-5.3.2/Zend/zend_vm_execute.h:104
warning: Source file is more recent than executable.
104			if ((ret = EX(opline)->handler(execute_data TSRMLS_CC)) > 0) {
(gdb) p ret
$2 = 324245876
(gdb) p handler
$3 = {{name = 0x83abb54 "cdb", flags = 31, open = 0x80c3150 <dba_open_cdb>, close = 0x80c30e0 <dba_close_cdb>, fetch = 0x80c2fe0 <dba_fetch_cdb>, 
    update = 0x80c2f70 <dba_update_cdb>, exists = 0x80c2f10 <dba_exists_cdb>, delete = 0x80c2af0 <dba_delete_cdb>, firstkey = 0x80c2d50 <dba_firstkey_cdb>, 
    nextkey = 0x80c2be0 <dba_nextkey_cdb>, optimize = 0x80c2b00 <dba_optimize_cdb>, sync = 0x80c2b10 <dba_sync_cdb>, info = 0x80c2b20 <dba_info_cdb>}, {
    name = 0x83abcc1 "cdb_make", flags = 31, open = 0x80c3150 <dba_open_cdb>, close = 0x80c30e0 <dba_close_cdb>, fetch = 0x80c2fe0 <dba_fetch_cdb>, 
    update = 0x80c2f70 <dba_update_cdb>, exists = 0x80c2f10 <dba_exists_cdb>, delete = 0x80c2af0 <dba_delete_cdb>, firstkey = 0x80c2d50 <dba_firstkey_cdb>, 
    nextkey = 0x80c2be0 <dba_nextkey_cdb>, optimize = 0x80c2b00 <dba_optimize_cdb>, sync = 0x80c2b10 <dba_sync_cdb>, info = 0x80c2b20 <dba_info_cdb>}, {name = 0x83abcca "db4", 
    flags = 15, open = 0x80c3390 <dba_open_db4>, close = 0x80c3320 <dba_close_db4>, fetch = 0x80c3a40 <dba_fetch_db4>, update = 0x80c39a0 <dba_update_db4>, 
    exists = 0x80c38f0 <dba_exists_db4>, delete = 0x80c3890 <dba_delete_db4>, firstkey = 0x80c3810 <dba_firstkey_db4>, nextkey = 0x80c3720 <dba_nextkey_db4>, 
    optimize = 0x80c32b0 <dba_optimize_db4>, sync = 0x80c32c0 <dba_sync_db4>, info = 0x80c32f0 <dba_info_db4>}, {name = 0x83abb58 "inifile", flags = 95, 
    open = 0x80c4470 <dba_open_inifile>, close = 0x80c4440 <dba_close_inifile>, fetch = 0x80c4180 <dba_fetch_inifile>, update = 0x80c4300 <dba_update_inifile>, 
    exists = 0x80c4240 <dba_exists_inifile>, delete = 0x80c40e0 <dba_delete_inifile>, firstkey = 0x80c4080 <dba_firstkey_inifile>, nextkey = 0x80c4000 <dba_nextkey_inifile>, 
    optimize = 0x80c3fb0 <dba_optimize_inifile>, sync = 0x80c3fc0 <dba_sync_inifile>, info = 0x80c3fd0 <dba_info_inifile>}, {name = 0x83abcce "flatfile", flags = 223, 
    open = 0x80c3eb0 <dba_open_flatfile>, close = 0x80c3e50 <dba_close_flatfile>, fetch = 0x80c3d10 <dba_fetch_flatfile>, update = 0x80c3d90 <dba_update_flatfile>, 
    exists = 0x80c3cb0 <dba_exists_flatfile>, delete = 0x80c3c70 <dba_delete_flatfile>, firstkey = 0x80c3bf0 <dba_firstkey_flatfile>, nextkey = 0x80c3b70 <dba_nextkey_flatfile>, 
    optimize = 0x80c3b20 <dba_optimize_flatfile>, sync = 0x80c3b30 <dba_sync_flatfile>, info = 0x80c3b40 <dba_info_flatfile>}, {name = 0x0, flags = 0, open = 0, close = 0, 
    fetch = 0, update = 0, exists = 0, delete = 0, firstkey = 0, nextkey = 0, optimize = 0, sync = 0, info = 0}}
(gdb) p execute_data
$4 = (zend_execute_data *) 0x8942960
(gdb) p * execute_data
$5 = {opline = 0x0, function_state = {function = 0x2, arguments = 0x0}, fbc = 0x1, called_scope = 0x8ac2d88, op_array = 0xb75f2690, object = 0x0, Ts = 0x0, CVs = 0x0, 
  symbol_table = 0xb75f2690, prev_execute_data = 0x0, old_error_reporting = 0x89429cc, nested = 188 '\274', original_return_value = 0x0, current_scope = 0xbfffcf78, 
  current_called_scope = 0x0, current_this = 0x13e9d700, current_object = 0x0, call_opline = 0x9aa1544}