When NERDTree is open; opening a file in a vertical split resizes the buffer strangely

vim-command-t-bug.md

##To reproduce:

• Open vim
• Open NERDTree
• Open a file
• At this point Vim looks like this screenshot
• Open Command-T, select a file, and press . This opens the file in a vertical split.
• At this point Vim looks like this screenshot
• Stay in that right-most vertical split.
• Open Command-T, select a file, and press . This opens the file in the right-most vertical split (since it's active).
• At this point Vim looks like this screenshot

##Actual Result:

The right-most vertical split has been resized strangely, almost as if the size of the NERDTree buffer was used to size it.

##Expected Result:

The right-most vertical split maintains it's current size.