What would cause empty output cache? And how to fix it?

Hi,

IPython3 worked fine so I installed jupyter, qtconsole. While I was 
using jupyter, qtconsole back and forth, I noticed qtconsole stopped 
showing [Out ##] prompt. It only showed the output result of input cell.

And IPython 4.0.1 also stopped caching output cells and I couldn't use 
the default variables, _, __, ___, and _[number].

I played with configuration variables that related to caching and 
history for hours in vain. Reinstallation of IPython 4.0.1 fixed it 
anyway.

@-MinRK


>    python3 -m pip install ipython
I managed to install ipython 4.0.1 after spending hours. I used pip3 
install [module] method.
http://wp.me/p1fjgj-1ZT