Array operations, dynamic arrays and length

[ixid via Digitalmars-d-learn]

	int[] a = [1,1,1,1];
	int[] b = [1,1,1,1];
	int[] c;

	c[] = a[] - b[];

	c.writeln;

This outputs []. This feels wrong, it feels like something that 
should have exploded or set the length to 4. If the lengths of a 
and b are mismatched it throws an exception. It also throws an 
exception if a dynamic array is longer or a static array is not 
the same length but is happy when a dynamic array is shorter. Is 
this intended behaviour and if so why?