Pointer dereference after ifstmt reads the wrong value

[wallds]

test.cpp

#include <Windows.h>
#include <stdint.h>

int main()
{
    const char* data = "0123456789";
    uint64_t target = 0;
    WriteProcessMemory(GetCurrentProcess(), &target, data, 8, NULL);
}

bug.d

#pragma D option quiet

syscall::NtWriteVirtualMemory:entry
/execname == $1/
{
    if (arg2) {
        printf("NtWriteVirtualMemory\n");
        printf("Buffer Address 0x%p\n", arg2);
        this->p = (uint64_t *)copyin(arg2, 8);
        printf("A 0x%llx\n", *this->p);
        printf("B 0x%llx\n", *this->p);
        if (1) {}
        printf("C 0x%llx\n", *this->p);
    }
}

syscall::NtTerminateProcess:entry
/execname == $1/
{
    exit(0);
}

dtrace -s bug.d test.exe

C expected value is 0x3736353433323130