implicit conversion & associative array.

[funog]

"Mutable and invariant types can be implicitly converted to const."

int[int] array;
const(int[int]) a = array;

outputs:
cannot implicitly convert expression (array) of type int[int] to const(int[int])

int[int] array;
const(int[int]) a = cast(const)array;

Compiles OK. ( DMD2.010 )

Where is my implicit conversion? ^^