Comment 4 for bug 1598999

fujiwarat posted a workaround for this issue at https://github.com/ibus/ibus/issues/1874#issuecomment-259625488. To apply it on your Linux Mint 18 box, you simply do the followings:

1. Rename /usr/lib/ibus-ui-gtk3 to /usr/lib/ibus-ui-gtk3.orig.
2. Edit the file /usr/share/ibus/component/gtkpanel.xml, and change the line
        <exec>/usr/lib/ibus/ibus-ui-gtk3</exec>
   to
        <exec>/usr/lib/ibus/ibus-ui-gtk3.orig</exec>
3. Log out and log in again.

With this workaround, I now leave the "Show property panel" setting to be "Always" without any problem.