If both, completeopt=menu,preview and cursorcolumn are set, the completion menu 
will vanish upon the first completion choice that would bring up the preview 
window. The preview window still works and is browseable, the menu still is 
gone, though.

The bug has bitten other people too:
https://github.com/Rip-Rip/clang_complete/issues/6
http://leetless.de/vimrc.txt

To reproduce, follow this (will assume installed python completion support):
1) Open a new python file with vim
1) a) vim foo.py
2) Set completion
2) a) filetype plugin on
2) b) set omnifunc=pythoncomplete#Complete
2) c) set completeopt=menuone,menu,longest,preview
3) Set cursorcolumn
3) a) set cursorcolumn
4) Import some stdlib that has docstrings

import string
foo = ""
foo.

5) Press <C-X><C-O>
6) Choose from list
7) Menu will vanish

The last rev I tested this on was 177 and there don't seem to be any relevant 
changes since then.

Hopefully that's helpful.