Running out of memory

[FG]

On 2012-12-27 16:31, bearophile wrote:
> Don't cast arrays arrays to pointers, it's unclean, because dynamic arrays are
> two words long. Use the .ptr property:
>
> GC.free(s.ptr);

Things appeared sorted out, but it's not over yet. delete still wins.
Performance-wise free() worked like delete, but there's a nasty glitch.
The following code crashes after a few hundred loops with
core.exception.InvalidMemoryOperationError.

     import std.stdio, core.memory;
     char[1000] filler = '.';
     int fill_times = 10000;
     void main(string[] args) {
         char[] s;
         for (int i=0; i < 100000; i++) {
             for (int j=0; j < fill_times; j++)
                 s ~= filler;
             writeln("loop ", i + 1, ", length: ", s.length);
             stdout.flush();
             // delete s;
             GC.free(s.ptr);
             s = [];
         }
     }


Surprisingly, when fill_times >= 3736, it always crashes after the 341th loop 
(relies on the filler having 1000 bytes. Some other numbers also trigger it).
What could be responsible for this odd behavior of free()?