I noticed that when you have for example v4.0.812.2 installed in directory
C:\Program Files\JetBrains\ReSharper\v4.0.812.2\ that an upgrade will be
installed by default in the same directory so it is possible that if you
install v4.0.816.4 that you install it in the v4.0.812.2 directory.
This is not a big issue as you can easily change the installation directory
manually but a better experience would be to install it in a directory named
after the version number you are trying to install.