Looks weird! but Joomla did it consistently after the same action carried out, i.e. redirecting to a page after saving. Checked everything but could not found any hint. Here is the code.
Every time this code executes, Joomla logout me from administration and when I login again, I do not have any admin functions available. I have to logout again and login to get full functionality. Strangely similar code works fine with other function. I do not have any clue until I discovered it is the problem with the language string COM_MYCOMPPONENT_SUCCESS.
The issue is the translation of that string contain some strange characters which came because the translation is not saved with utf-8 encoding. Updated the string, voila! it works now :) . Hope it helps someone stumble upon with same issue.