If two classes alias this each other and their is an unknown identifier DMD will fail with segmentation fault: 11. This is on DMD 2.061, Mac OS X 10.8.2.

Example:

class foo {
	bar fun;
	alias fun this;

	this() {
		fun = new bar(this);
		fun.a = 5; //remove this line and the program will compile.
	}
}

class bar {
	foo sun;
	alias sun this;

	this(foo t) {
		sun = t;
	}
}

void main() {
	foo fun = new foo;
}