An example that actually compiles would help your case.

It's purely theoretical. You shouldn't have to compile it to see that it will crash.

The buffer will be filled with unknown data after the first two known values so the four bytes at BYTE *data will be some random value which surely will not be the desired pointer value.
The zero sized array version ->data member will always point to the next byte after the known values in the buffer.

All I see is undefined behavior from using a bogus pointer. I have debugged many cases where the same problem does not crash, so your theoretical result does not mean anything unless you can back it up with empirical data. The problem is that saying things like this will crash gives beginners a false sense of security that the program will fail spectacularly if they do something wrong. It is just as probable that the program will fail silently and continue running until the damage done is very costly.

Agreed. Saying it will crash is highly subjective.

I will try to avoid that in the future. I forget that what's 'obvious' to me is not to every one

We all do. For me, obvious now is not always obvious later too.