Is the interrupt_ethernet example correct?

On this manual page: http://www.keil.com/support/man/docs/rlarm/rlarm_interrupt_ethernet.htm

        frame = alloc_mem (RxLen | 0x80000000);
        /* if 'alloc_mem()' has failed, ignore this packet. */
        if (frame != NULL) {
          dp = (U32 *)&frame->data[0];
          sp = (U32 *)Rx_Desc[idx].Packet;
          for (RxLen = (RxLen + 3) >> 2; RxLen; RxLen--) {
            *dp++ = *sp++;
          }

Shouldn't the size of the allocated memory be RxLen + 4 because the type of the data pointed to is

typedef struct os_frame
    U16 length;
    U16 index;
    U8 data[1];
} OS_FRAME;

and dp points to the member data, which is 4 bytes after the beginning of the struct?