c - sscanf to uint8_t behaves different depending on variable order in structure body

Question

I've encountered strange behaviour when using sscanf. Depending on order of a and b in structure one of them is getting 0.

typedef struct MyStructure{
    uint8_t  a;
    uint8_t  b;
}MyStructure;

and here is code which gets me confused:

if (2 == sscanf(rawCommand,"%*s %*s %"SCNu8" %"SCNu8"", &a, &b)){
    ... some code
}

When I change order of variables in structure body to:

typedef struct MyStructure{
    uint8_t  b;
    uint8_t  a;
}MyStructure;

sscanf returns 2 but a is 0;

I've tested it on 32bit GCC on linux and above code works in both ways. But when compiling with 64bit GCC on windows 7 it behaves like I mentioned. On boths systems I'm using GCC 4.8.1.