Immutable cannot be casted to const when using pointers

[Jeroen Bollen]

For some reason this code doesn't work...

module app;

void main() {
	immutable char var = 'a';
	immutable(char)* varPtr = &var;
	test(&varPtr);
}

void test(immutable(char)** param) {
	test2(param);
}

void test2(const(char)** test2) {
	
}

It'll give you " Error: function app.test2 (const(char)** test2) 
is not callable using argument types (immutable(char)**)", which 
makes no sense as if a function requests a constant variable, 
immutable should suffice.

What's even weirder (although it is what should happen), if you 
remove one of the pointers, it compiles fine.

module app;

void main() {
	immutable char var = 'a';
	test(&var);
}

void test(immutable(char)* param) {
	test2(param);
}

void test2(const(char)* test2) {
	
}

Is this a bug? I'm using DMD.