Undefined property notice

PHP have the Undefined variable/property notice to inform a programmer about using uninitialized variables/properties. While both $b = $b + 5 and $c += 5 issues the notice (and also $a["b"] = $a["b"] + 5 and $a["c"] += 5 in case of arrays), in case of objects only $o->b = $o->b + 5 issues the notice but $o->c += 5 not. Shouldn't be the notice issued also with $o->c += 5? It is clearly usage of an undefined property. Jakub Vrana