SMIE default syntax : First level of indentation

Question

When you only do that in your major mode :

(require 'smie)
(smie-setup nil #'ignore)

That means SMIE but no grammar, and no rules. And it's great. It makes the point stay on col0 when you TAB and there's nothing on the line, it makes indentation basically sane and logic for a c-like major mode derived from fundamental-mode.

Except for this weird detail : The first indentation level is messed up :

plop = {
    plop;
        plop;
        plop;
        plop;
}

Is that a bug? It looks like a bug. And if it's not, how can I make it so that :

plop = {
    plop;
    plop;
    plop;
    plop;
}