A web application can leverage "immutable" session attributes for one of two purposes:

1. For genuine immutable attributes, to avoid an implicit write following an explicit read
2. For mutable attributes to be treated as immutable, replacing implicit writes on every request with explicit writes only when needed

WFLY-18572 mistakenly skipped writes if the object reference passed to setAttribute(...) is the same as the existing attribute. This precludes #2 above.