When there is a failure in the installation process (for example if DocNav is running at background), the installer fails to clean up the partially installed files after I select cancel installation.
When I attempt to install again to the same location, the installation fails, saying that Vivado 2014.1 is already installed.
Because not every file is being properly deleted, the install directory will exist and is therefore flagged by the subsequent install as "Already existing" even though it is not fully populated.
You will need to delete these files and directories (for example C:\Xilinx\Vivado\2014.1 and any residual content) manually before rerunning installation.
In most cases the installer cleans up and leaves an empty directory.
However, in a case where the directory is not fully cleaned up, the installer pop up a message at the end that some files not removed and ask user to remove them manually.
Note: From Vivado 2014.2 onward, the installer will not let you proceed if DocNav is open.