What's compiler thinking about the switch-statement?

Inspired from a -5 question again!

• Is empty case of switch in C# combined with the next non-empty one?

I read [this comment] of @Quartermeister and been astonished!

So why this compiles

switch(1) {
    case 2:
}

but this doesn't.

int i;

switch(i=1) {
    case 2: // Control cannot fall through from one case label ('case 2:') to another
}

neither this

switch(2) {
    case 2: // Control cannot fall through from one case label ('case 2:') to another
}

update:

The -5 question became -3.