问题
In VIM I've got 4 windows opened and a NERD tree like this:

UPD: It looks like the problem is in hidden buffers. When the buffer was opened in one window, and then replaced by another - if you try to open the very first in another window, you'll get it opened in the window it was opened in the very first time.
回答1:
I'm using NERD tree 4.1.0 on Vim 7.2 and NERDTree does open files in the last active window by default.
From the docs:
Default key: o
Map option: NERDTreeMapActivateNode
Applies to: files and directories.
If a file node is selected, it is opened in the previous window.
But hitting enter when the file is selected has the same effect.
来源:https://stackoverflow.com/questions/3607718/open-file-from-nerdtree-in-specific-window-or-last-active