alpine musl pthread_key_create bug

test.c

#include<stdio.h>
#include<pthread.h>
#include<assert.h>

/*
 * first pass succeeds
 *
 * second pass succeeds on:
 *   Debian 9
 *   Ubuntu 18.10
 *   CentOS 7
 *   Mac OS X 10.13.6
 *   OpenBSD 6.3
 *
 * but fails on Alpine 3.8.1 / musl 1.1.19-r10:
 *
 * the first call to pthread_getspecific() after key creation returns the value set
 * by the previous pass, instead of NULL. According to spec, I believe this to be
 * incorrect behavior:
 *  http://pubs.opengroup.org/onlinepubs/007904975/functions/pthread_key_create.html
 *
 * Possibly related issues:
 *  https://www.google.com/search?q=%22lmdb%22+%22MDB_BAD_RSLOT%22+%22alpine%22
 *
 * compile with -DWORKAROUND to clear key value before deleting
 */

#ifdef WORKAROUND
#define pthread_key_delete(key) (pthread_setspecific((key), NULL),pthread_key_delete((key)))
#endif

/*
 * create a new tls key
 * ensure current value is NULL
 * set a new value
 * ensure current value was correctly updated
 * delete tls key
 */
void test(char *label){
	int rc;
	pthread_key_t key;
	void *ptr = (void *)test;

	fprintf(stderr, "%s\n", label);

	rc = pthread_key_create(&key, NULL);
	assert(!rc);

	void *val = pthread_getspecific(key);
	assert(!val);

	rc = pthread_setspecific(key, ptr);
	assert(!rc);

	val = pthread_getspecific(key);
	assert(val == ptr);

	rc = pthread_key_delete(key);
	assert(!rc);
}

int main(int argc, char **argv){
	test("pass 1");
	test("pass 2");
	return 0;
}