writeln wipes contents of variables ?

[W.J. via Digitalmars-d-learn]

Hi everybody!

I'm new to D and trying to wrap my head around ranges.

For a start I'm trying to take a input string and transform it, 
group it, etc.
After each step I inspect the result.
It works fine until step 3 where all of a sudden, after 
write(ln)ing the result, "step3" holds an array of empty arrays.
What gives? Program and output are attached below.

My question is why are "step3"'s contents before and after the 
writeln (1) different?
If I remove this line at (1) the foreach loops print the contents 
as I'd expect and the following writeln (2) prints the contents 
as expected, too.
However the writeln (3) prints empty arrays again.
I don't understand this behavior and I'd really like to know 
what's going on.

Your help and time is much appreciated!

I'm using an unmodified local build of dmd, druntime, and phobos 
from github updated and recompiled today.

[code]
import std.range;
import std.stdio;
import std.algorithm;

void main() {
   string test = "@\r  node1\n    nodea\r\n    key:val\n\n  
node2\n    nodea\n";
   writeln(test);
   writeln("---");

   auto step1 = test.replace("\r\n", "\n")
                 .replace("  ", "\t")
                 .splitter!"a == 10 || a == 13"()
                 ;
   writeln("Step 1:", step1);
   writeln("---");
   writeln("  type: ", typeid(step1));
   writeln("---");

   import std.typecons: Tuple;
   string[][] step2;
   foreach(a; step1) {
     auto e = findSplitAfter(a, "\t").array;
     step2 ~= e;
   }
   writeln("Step 2:", step2);
   writeln("---");
   writeln("  type: ", typeid(step2));
   writeln("---");

   auto step3 = step2.chunkBy!((a,b) => a[0]==b[0]).array;
   writeln("Step 3:", step3); // (1)
   writeln("---");
   writeln("  type: ", typeid(step3));
   writeln("-+-");

   foreach(x; step3) {
     writeln("x:",typeid(x),x);
     foreach(y; x)
       writeln("  y:",typeid(y),y);
   }
   writeln("--",step3); // (2)
   writeln("--",step3); // (3)
   writeln("the end");
}
[/code]

Output:
[code]
   node1
     nodea
     key:val

   node2
     nodea

---
Step 1:["@", "\tnode1", "\t\tnodea", "\t\tkey:val", "", 
"\tnode2", "\t\tnodea", ""]
---
   type: std.algorithm.iteration.SplitterResult!(unaryFun, 
string).SplitterResult
---
Step 2:[["", "@"], ["\t", "node1"], ["\t", "\tnodea"], ["\t", 
"\tkey:val"], ["", ""], ["\t", "node2"], ["\t", "\tnodea"], ["", 
""]]
---
   type: immutable(char)[][][]
---
Step 3:[[["", "@"]], [["\t", "node1"], ["\t", "\tnodea"], ["\t", 
"\tkey:val"]], [["", ""]], [["\t", "node2"], ["\t", "\tnodea"]], 
[["", ""]]]
---
   type: app.main.ChunkByImpl!(__lambda1, 
string[][]).ChunkByImpl.Group[]
-+-
x:app.main.ChunkByImpl!(__lambda1, string[][]).ChunkByImpl.Group[]
x:app.main.ChunkByImpl!(__lambda1, string[][]).ChunkByImpl.Group[]
x:app.main.ChunkByImpl!(__lambda1, string[][]).ChunkByImpl.Group[]
x:app.main.ChunkByImpl!(__lambda1, string[][]).ChunkByImpl.Group[]
x:app.main.ChunkByImpl!(__lambda1, string[][]).ChunkByImpl.Group[]
--[[], [], [], [], []]
the end
[/code]