Can't call splitter with range struct

[David Skluzacek via Digitalmars-d-learn]

I came across this problem as I was trying to see if could write 
a quick range-based solution with std.zlib to do what was asked 
about in a different Learn forum post - read a gzipped file.

This seems like it should work:
import std.stdio, std.algorithm, std.zlib;
import std.range.primitives;

void main(string[] args)
{
    auto f = GZippedFile(File(args[1], "rb"));
    f.splitter("\n").each!writeln;
}

struct GZippedFile
{
    File file;
    UnCompress uncompressor;
    ubyte[] readBuffer;
    const(char)[] buffer;

    this(File f) {
        file = f;
        uncompressor = new UnCompress(HeaderFormat.gzip);
        readBuffer = new ubyte[4096];
    }

    dchar front() const {
        return buffer.front;
    }

    void popFront() {
        if (buffer.empty) {
            buffer = cast(const(char)[])
                uncompressor.uncompress(file.rawRead(readBuffer));
        }
        else {
            buffer.popFront();
        }
    }

    bool empty() {
        return buffer.empty && file.eof();
    }
}

But I get:

Error: template std.algorithm.iteration.splitter cannot deduce 
function from argument types !()(GZippedFile, string), candidates 
are:
/usr/include/dlang/dmd/std/algorithm/iteration.d(4678):        
splitter(alias pred = "a == b", Range, Separator)(Range r, 
Separator s)
  with pred = "a == b",
       Range = GZippedFile,
       Separator = string
  must satisfy the following constraint:
       is(typeof(binaryFun!pred(r.front, s)) : bool)
(...)

If I change the newline separator to a character literal, I get:

(...)
/usr/include/dlang/dmd/std/algorithm/iteration.d(5055):        
splitter(alias pred = "a == b", Range, Separator)(Range r, 
Separator s)
  with pred = "a == b",
       Range = GZippedFile,
       Separator = char
  must satisfy the following constraint:
       is(typeof(binaryFun!pred(r.front, s.front)) : bool)

It seems like "\n" should pass the second constraint and '\n' 
should pass the first.  Using a dchar or dstring makes no 
difference. Adding @property to front makes no difference. Is 
this a bug?