Actually PHP version is not irrelevannt, as well as - this infos 

- TS or NTS
- --enable-zend-signals used while configured

Could you provide your phpinfo() and may be a way to reproduce?

I don't have a ready-made test case for this, because it involves a local modification to PHP which predates Zend signals.  It was a NTS build (Apache prefork) if that matters.  Before I go through the trouble of creating a test case (*** see note below) for something which is obvious through code reading, here is the excerpt (APC-3.1.11 beta) that I'm referring to:

int _apc_store(char *strkey, int strkey_len, const zval *val, const unsigned int ttl, const int exclusive TSRMLS_DC) {
...
...
    HANDLE_BLOCK_INTERRUPTIONS();

    APCG(current_cache) = apc_user_cache;

    ctxt.pool = apc_pool_create(APC_SMALL_POOL, apc_sma_malloc, apc_sma_free, apc_sma_protect, apc_sma_unprotect TSRMLS_CC);
    if (!ctxt.pool) {
        // XXX Need to HANDLE_UNBLOCK_INTERRUPTIONS()
        // XXX (Maybe?) Need to NULL out APCG(current_cache)?
        apc_warning("Unable to allocate memory for pool." TSRMLS_CC);
        return 0;
    }


*** It takes some effort to force apc_pool_create() to fail.  In my particular instance, the SMA spinlock acquisition timed out during a nightly virtual machine snapshot.