Shaon,
I have links to screenshots to perhaps better troubleshoot this issue.
Background:
Again this exact same process works well on wordpress 3.5 with no issue.
Setup new wordpress install 3.6.1 on localhost using wamp server.
Selected 2012 template
Screenshot: https://s17.postimg.org/z1mvxf3xr/Theme.png
Removed all plugins
Installed/activated Page layout builder/minimax
Screenshot: https://s21.postimg.org/4xw1r63nb/Plugins.png
Create new page and select minimax tab
Insert 1 Col row and add Rick Text Module
The result is as shown in the following screenshot:
https://s17.postimg.org/cfm5yfflb/rich_text.png
In the bottom wysiwyg “a123” is auto populated. I did not add that.
Let me know if there is anything else I can do to help this process along. Feel free to post your email address if you would like for me to email you directly.