[LeakSanitizer] valid pointer re-used after huge realloc()

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int
main(void)
{
    char *ptr = malloc(1000000);
    if (ptr == NULL) {
        fprintf(stderr, "error: out of memory\n");
        exit(1);
    }
    ptr[0] = 'a';

    char *a = realloc(ptr, 842105263157894744ULL);
    if (a != NULL) { /* allocation is supposed to fail */
        fprintf(stderr, "error: huge allocation unexpectedly worked\n");
        exit(1);
    }
    /*
     * At this point a==NULL. The original pointer is still valid according
     * to the C standard!
     */

    /* new allocation */
    char *b = malloc(1000000);
    if (b == NULL) {
        fprintf(stderr, "error: out of memory\n");
        exit(1);
    }
    b[0] = 'b';

    if (ptr[0] == 'b') { /* The new allocation re-used the valid ptr! */
        fprintf(stderr, "error: pointer handed out twice!\n");
        exit(1);
    }

    free(b);
    free(ptr);

    return 0;
}

$ export LSAN_OPTIONS="allocator_may_return_null=1"
$ /home/stefan/clang/bin/clang -Wall -Wextra -fsanitize=leak -o realloc realloc.c 
$ ./realloc 
==24104==WARNING: LeakSanitizer failed to allocate 0xbafc24672035e58 bytes
error: pointer handed out twice!

$ export ASAN_OPTIONS="allocator_may_return_null=1:detect_leaks=1"
$ /home/stefan/clang/bin/clang -Wall -Wextra -fsanitize=address,leak -o realloc realloc.c 
$ ./realloc 
==24114==WARNING: AddressSanitizer failed to allocate 0xbafc24672035e58 bytes

$ /home/stefan/clang/bin/clang -Wall -Wextra -o realloc realloc.c
$ valgrind ./realloc 
==24123== Memcheck, a memory error detector
==24123== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==24123== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
==24123== Command: ./realloc
==24123== 
==24123== 
==24123== HEAP SUMMARY:
==24123==     in use at exit: 0 bytes in 0 blocks
==24123==   total heap usage: 3 allocs, 3 frees, 842,105,263,159,894,744 bytes allocated
==24123== 
==24123== All heap blocks were freed -- no leaks are possible
==24123== 
==24123== For counts of detected and suppressed errors, rerun with: -v
==24123== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)