SList!(Tuple!int) == error?

[Mehrdad]

Why is it an error to have a singly-linked list of Tuple!(int)?
phobos\std\container.d(938):
Error: function
std.typecons.Tuple!(int).Tuple
.opEquals!(const(Tuple!(int)))
.opEquals (const(Tuple!(int)) rhs)
is not callable using argument types
(const(Tuple!(int))) const
Error: template instance std.container.SList!(Tuple!(int)) error 
instantiating