GVim accepts extra text from ibus when not in paste mode

I'm using ibus to enter Japanese text into GVim.

For example, if I want to enter the word 家庭 (katei), I follow the steps below:

1) Switch to input mode (press i)
2) Switch on IME (using the appropriate key combination)
3) Enter the letters: k a t e i
4) Ibus will show a couple of candidates for the word (過程　仮定　家庭). In all other programs, I can highlight them by pressing up/down arrows, and make my selection by pressing Enter. However, in GVim, it enters the text without me pressing Enter, so I end up with a mess like 過程仮定家庭.

If I enable paste mode in GVim (set paste), then the problem goes away.

Here are my system details. Please let me know if there is any other information I can provide.

GVim version: 7.3.429
ibus-daemon - Version 1.4.1
Ubuntu 12.04
Fluxbox desktop manager

misha@misha-lmd:~/git/iwait2013/doc$ lsb_release -rd
Description: Ubuntu 12.04.1 LTS
Release: 12.04
misha@misha-lmd:~/git/iwait2013/doc$ apt-cache policy vim
vim:
  Installed: 2:7.3.429-2ubuntu2.1
  Candidate: 2:7.3.429-2ubuntu2.1
  Version table:
 *** 2:7.3.429-2ubuntu2.1 0
        500 http://jp.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     2:7.3.429-2ubuntu2 0
        500 http://jp.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages
misha@misha-lmd:~/git/iwait2013/doc$ apt-cache policy ibus
ibus:
  Installed: 1.4.1-3ubuntu1
  Candidate: 1.4.1-3ubuntu1
  Version table:
 *** 1.4.1-3ubuntu1 0
        500 http://jp.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages
        100 /var/lib/dpkg/statu