Serialising ConcurrentDictionary causes .NET framework error

[Svet3]

The following minimal program shows up an obscure issue I ran into by accident;

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using JsonFx.Json;
namespace JsonFXTest{
class Program{
static void Main(){
IDictionary<int, object> dict = new ConcurrentDictionary<int, object>();
dict.Add(1, new object());
string json = new JsonWriter().Write(dict);
Console.WriteLine(json);
}}}

Executing this terminates the program at the serialisation step with no stack trace and the following Error events added to the Application event log;

<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
<System>
<Provider Name=".NET Runtime" />
<EventID Qualifiers="0">1023</EventID>
<Level>2</Level>
<Task>0</Task>
<Keywords>0x80000000000000</Keywords>
<TimeCreated SystemTime="2016-05-27T16:24:28.442474700Z" />
<EventRecordID>139541</EventRecordID>
<Channel>Application</Channel>
<Security />
</System>
<EventData>
<Data>Application: JsonFXTest.exe Framework Version: v4.0.30319 Description: The process was terminated due to an internal error in the .NET Runtime at IP 00007FFB999612E0 (00007FFB99960000) with exit code 80131506.</Data>
</EventData>
</Event>

<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
<System>
<Provider Name="Application Error" />
<EventID Qualifiers="0">1000</EventID>
<Level>2</Level>
<Task>100</Task>
<Keywords>0x80000000000000</Keywords>
<TimeCreated SystemTime="2016-05-27T16:24:28.474494500Z" />
<EventRecordID>139542</EventRecordID>
<Channel>Application</Channel>
<Security />
</System>
<EventData>
<Data>JsonFXTest.exe</Data>
<Data>1.0.0.0</Data>
<Data>574874b5</Data>
<Data>clr.dll</Data>
<Data>4.6.1080.0</Data>
<Data>570c4ace</Data>
<Data>c0000005</Data>
<Data>00000000000012e0</Data>
<Data>605c</Data>
<Data>01d1b8343db84f3e</Data>
<Data>c:\WorkingArea\scratch-code\JsonFXTest\bin\Debug\JsonFXTest.exe</Data>
<Data>C:\Windows\Microsoft.NET\Framework64\v4.0.30319\clr.dll</Data>
<Data>72f2ac39-d181-4bae-88b5-b809aca8f10f</Data>
<Data />
<Data />
</EventData>
</Event>

I was using JsonFX v2.0.1209.2802 on .Net 4.5.2 and it happens in both 32 and 64 bit