TGA File Header is not correct on Windows

I'm trying to read a TGA header of the file i created in Paint.net, and it seems that there is something wrong with it. If I use the header structure from the speciffication, like this one:

typedef struct {
    CHAR  idlength;
    CHAR  colourmaptype;
    CHAR  datatypecode;
    WORD colourmaporigin;
    WORD colourmaplength;
    CHAR  colourmapdepth;
    WORD x_origin;
    WORD y_origin;
    WORD width;
    WORD height;
    CHAR  bitsperpixel;
    CHAR  imagedescriptor;
} TGAHEADER;

I get this:

Data size: 0
Color Map type: 0
Data Type code: 2
Bits per-pixel: 0
Size: 501 x 2080

Which is wrong, since my image is 501x501, 32-bits per pixel. However if I comment out two bytes from the sturcture, f.e. this one colourmaporigin, I get this:

Data size: 0
Color Map type: 0
Data Type code: 2
Bits per-pixel: 32
Size: 501 x 501

Which is correct. I was reading everything I found on this file format, and it never says that any of those fields are optional or something.

How come I get results like this?

Here's the code for reading the data:

void Image::readTGA()
{
    TGAHEADER fileHeader;

    std::ifstream fileHandle(fileName, std::ios::binary);
    if (fileHandle.is_open())
    {
        fileHandle.read((char*)(&fileHeader), sizeof(TGAHEADER));
        fileHandle.close();
    }
    else
    {
        std::cout << "An error occured when opening a file." << std::endl;
    }
}