This occurs with statically or dynamically linked modules, but I am only experiencing it myself with dynamically linked extensions. I have configured PHP to load two extensions I have created at run time, let's call them A and B. A relies on behaviour of B. I have ordered them in the php.ini file so that A is before B, and thus A gets initialized before B (which is required for B to work properly). However, on shutdown, A is also shutdown before B, and since B requires A to be still running to shut down, there is a core dump.

Modules should be getting shut down in the reverse order that they are started, to preserve dependencies.

I've actually patched this myself, here is the simple fix:

Zend/zend_hash.c
539c539
<       p = ht->pListHead;
---
>       p = ht->pListTail;
542c542
<               p = p->pListNext;
---
>               p = p->pListLast;