UML24 — Association owned derived union

Is it really illegal to define a non-navigable association-owned property as derived union?

When I try that I invalidate the following constraint in section 7.3.44 the metamodel:

[6]Only a navigable property can be marked as readOnly.
isReadOnly implies isNavigable()

Why "efficiency of access" (as implied by navigability) restrics read-only access?

One way to get around that is to make the property owned in the "navigableOwnerEnd" vs. "ownedEnd" of the association? do we have any precedence of doing that in an abstract syntax?

This constraint seems to be an old constraint from UML 1.x when navigability meant the same as ownership of property. It is not consistent with the meaning of navigability now, which is about “efficiency of access”.