It's not a reduced test case, but the following program seg faults:

import std.stdio,
	std.algorithm,
	std.range;

void main()
{
 	int i = 1;
	auto arr = zip([0, 1, 2], ["A", "B", "C"]);

	// Works fine
	writeln(
		filter!((a){ return a[0] > 1; })(arr)
	);

	// Seg faults
	writeln(
		filter!((a){ return a[0] > i; })(arr)
	);
}

The only difference between the two delegate literals is that the second references a variable (i) in the enclosing scope, while the first only compares against a literal. This is leads me to suspect bad code for the closure which is being created. Curiously, I've only been able to reproduce this when using std.range.zip as the range to operate on.