You are writing one location past what you own. (See @Oli Charlesworth comment)
for (i = 0; i < stress_size; ++i)
{
a++;
*a = 4; // Bad: Setting array a_original[1] to a_original[stress_size].
}
Change to:
for (i = 0; i < stress_size; ++i)
{
*a = 4; // Setting array a_original[0] to a_original[stress_size-1].
a++;
}
BTW: Do you want a lower l
here: printf("%Ld bytes allocated\n"...