Confused about class equality

[strtr]

The program below outputs, as I would expect :
Same Value.
Same Object.
3 : 44E15C 0000
3 : 44E15C 0000
5 : 44E15C 0000
5 : 44E15C 0000

Now what would it mean if it were to output :
Same Value.
3 : 5B536C 59D020
3 : 59CE0C 59CEF0
5 : 5B536C 59D020
5 : 59CE0C 59CEF0
(Output from essentially the same piece of code within a larger project)

Not the same object, but still able to change it with one call.
What is it I don't get?

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module main;

import std.stdio;
import std.string;

interface I{
	char[] toString();
	int value();
	void value(int v);
}

class C : I{
	private int _value;
	
	this(int v){ _value = v; }
	char[] toString(){ return format(_value); };
	int value(){ return _value; };
	void value(int v){ _value = v; };
}
private I[3][3] arr;

public I getI( int x, int y){ return arr[x][y]; }
public void setI( int x, int y, I i ){ arr[x][y]= i; }

void main(){
	C c = new C(3);
	setI( 0, 0, c );
	setI( 1, 2, c );
	I i1 = null;
	I i2 = null;
	i1 = getI(0,0);
	i2 = getI(1,2);
	
	if( i1 !is null && i2 !is null && i2.value == i1.value ) {
		writefln("Same Value.");
		if( i2 is i1 ) writefln("Same Object.");
		writefln( i2.toString()," : ",i2.__vptr," ",i2.__monitor);
		writefln( i1.toString(), " : ", i1.__vptr," ",i1.__monitor);
		i1.value = 5;
		writefln( i2.toString()," : ",i2.__vptr," ",i2.__monitor);
		writefln( i1.toString(), " : ", i1.__vptr," ",i1.__monitor);
	}
}