On the opposite, simply evaluating
    local.__dict__
just before "deadlist = ...", frees the last value.

Weird? I found that in threadmodule.c, the local object has a
"self->dict" attribute, which contains the last used dictionary. The
dictionaries switch when tp_getattro or tp_setattro are called from a
different thread.

Maybe localobject could be rewritten with no self->dict at all. Or make
self->dict a *borrowed* reference inside the array of thread-local
dictionaries.