StringBuilder.Append not working

Question

We have a WCF project where JSON responses are generated automatically but in one scenario we are creating the JSON manually and sending it to browser. That part works fine.

Last night I noticed a bug and tried to figure it out but the problem is really strange. Somehow after concatenating the string values, a block gets removed and I don't have an idea what happened here. See the following code, what is happening?

Following is the snapshot of JSON after the "innerBlock" return data

Following is the snapshot of JSON after string append!

Answer 1

The .Net application was working fine. Since, my JSON was too big, I was using some JSON viewers, but unfortunately they had bugs. Tested the JSON in notepad and things were working fine.

1. http://jsonviewer.stack.hu

2. http://jsonlint.com