I think there is no explicit support for tools like vcsh.

vcsh set's $GIT_DIR and in older versions $GIT_WORK_TREE. This breaks vundle, as each clone it runs is updating the main vcsh repo. In my case when I work on my vim-config I'm almost always inside my vcsh vimrc environment, which has the environment variables set, so a try to run :PluginInstall fails and messes up my main repository.

The obvious workaround is to run it outside the vcsh environment, but it forces one to use multiple terminals or rapidly exit and reenter the environment.