second message is lost

main.c

#include <stdio.h>

#include "vtimer.h"
#include "thread.h"
#include "msg.h"

char timer_stack[KERNEL_CONF_STACKSIZE_DEFAULT];

struct timer_msg {
	char* msg;
};

struct timer_msg msg_a = { .msg = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" };
struct timer_msg msg_b = { .msg = "BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB" };

void timer_thread(void) {
	printf("This is thread %d\n", thread_getpid());

	while (1) {
		msg_t m;
		msg_receive(&m);
		struct timer_msg* tmsg = (struct timer_msg*) m.content.ptr;
		puts(tmsg->msg);

		/* allow switching to main thread for next msg to be sent */
		vtimer_usleep(1000);
	}
}

int main(void) {
	msg_t m;
	int pid = thread_create(timer_stack, sizeof timer_stack, PRIORITY_MAIN-1, CREATE_STACKTEST, timer_thread, "timer");

	puts("sending 1st msg");
	m.content.ptr = (char*) &msg_a;
	msg_send(&m, pid, false);

	puts("sending 2nd msg");
	m.content.ptr = (char*) &msg_b;
	msg_send(&m, pid, false);
}