:cw messes with _ =

[Benji Fisher]

     After opening the quickfix window and using <C-W>_ to make it
larger, I find that <C-W>= no longer works until I close the quickfix
window.

Details:  vim 7.0 (no patches) on Linux + GTK2 (so 'encoding' is set to
utf-8) + Normal features (compiled OOTB).

$ vim -u NONE
:helpgrep guifont=\*
:cw
:wincmd _
:wincmd =

                                        --Benji Fisher