Readfile of serial GPS in VS2010 produces additional values

Question

I am writing a program to capture serial data from an old GPS unit (Garmin Etrex Venture) connected to a PC. After sending a 'send time' packet to the unit, I use a readfile from the COM3 port (hCom).

int read_packet()   //READS PACKET FROM DEVICE hPort
    {
        unsigned char inbuff[64]; 
        unsigned char inchar [1];
        DWORD nb;
        int j=0;
        ReadFile(hPort, inbuff, 32, &nb, NULL); int k; for (j;j<25;j++) {printf("<read_packet> inbuff[%i] = %i \n",j,int(inbuff[j]));

        //for (j=0;j<25;j++) {ReadFile(hPort, inchar, 1, &nb, NULL); printf("<read_packet> inchar[%i]: %i \n",j,int(inchar[0]));
        }
    return 0;
    }

Valid packets start with 0x10 and end in 0x10 0x03. I expect to see an ACK packet (0x06) and then a second packet containing the actual time.

When reading the data all in one go to inbuff, the read continues after the final 0x03 at inbuff[21] with what seem to be nonsense values:

<read_packet> inbuff[0] = 16
<read_packet> inbuff[1] = 6
<read_packet> inbuff[2] = 2
<read_packet> inbuff[3] = 10
<read_packet> inbuff[4] = 0
<read_packet> inbuff[5] = 238
<read_packet> inbuff[6] = 16
<read_packet> inbuff[7] = 3
<read_packet> inbuff[8] = 16
<read_packet> inbuff[9] = 14
<read_packet> inbuff[10] = 8
<read_packet> inbuff[11] = 9
<read_packet> inbuff[12] = 14
<read_packet> inbuff[13] = 225
<read_packet> inbuff[14] = 7
<read_packet> inbuff[15] = 22
<read_packet> inbuff[16] = 0
<read_packet> inbuff[17] = 12
<read_packet> inbuff[18] = 25
<read_packet> inbuff[19] = 176
<read_packet> inbuff[20] = 16
<read_packet> inbuff[21] = 3
<read_packet> inbuff[22] = 42
<read_packet> inbuff[23] = 0
<read_packet> inbuff[24] = 32

When I uncomment the second line and read one character at a time, I received the 2 packets expected (although keeps reading the final 0x03):

<read_packet> inchar[0]: 16
<read_packet> inchar[1]: 6
<read_packet> inchar[2]: 2
<read_packet> inchar[3]: 10
<read_packet> inchar[4]: 0
<read_packet> inchar[5]: 238
<read_packet> inchar[6]: 16
<read_packet> inchar[7]: 3
<read_packet> inchar[8]: 16
<read_packet> inchar[9]: 14
<read_packet> inchar[10]: 8
<read_packet> inchar[11]: 9
<read_packet> inchar[12]: 14
<read_packet> inchar[13]: 225
<read_packet> inchar[14]: 7
<read_packet> inchar[15]: 22
<read_packet> inchar[16]: 0
<read_packet> inchar[17]: 12
<read_packet> inchar[18]: 0
<read_packet> inchar[19]: 201
<read_packet> inchar[20]: 16
<read_packet> inchar[21]: 3
<read_packet> inchar[22]: 3
<read_packet> inchar[23]: 3
<read_packet> inchar[24]: 3

Can anyone advise why the first situation using inbuff happens? I guess that it happens because the Readfile does not know when to stop reading. However I don't understand where the additional values after inbuff[21] are coming from.

Thanks.