immutable shared not accepted as TypeCtor ?

[Basile B. via Digitalmars-d-learn]

----
void main()
{
     alias T = immutable(shared(int));
     static assert(is(T==immutable));
     static assert(is(T==shared));
}
----
It probably doesn't make sense to have immutable shared data but 
the grammar indicates that there can be many of them without any 
explicit restriction.


Is it a bug ?