Why can't I add back a git submodule after removing it

I tried deleting a submodule and then adding it back with git 1.8.5.2. An submodule `asub` was added by `git submodule add -b master url_asub.git`. I removed the submodule by ``` git rm asub ``` The asub directory is gone. I then tried to add it back again with the original command that added it (to test if the submodule removal in 1.8.5.2 is clean): ``` git submodule add -b master url_asub.git ``` I got an error message: ``` A git directory for 'asub' is found locally with remote(s): origin url_asub.git If you want to reuse this local git directory instead of cloning again from url_asub.git use the '--force' option. If the local git directory is not the correct repo or you are unsure what this means choose another name with the '--name' option. ``` I am not sure what this error message means. I also tried doing `git submodule sync` in the superproject, and tried ``` git submodule deinit asub git rm asub git submodule add -b master url_asub.git ``` But still I couldn't add the submodule back. What did I miss, or is this a bug in git 1.8.5.2? The reason I want to do this is to a) remove a submodule and b) add it back so that it reflects the most recent content of the submodule. This may sound naive but I found that the `submodule add -b` feature will break as soon as I clone the super project (how to keep git submodule on-branch status after cloning superproject?). So I figured probably a simply way to avoid all the troubles of keeping submodules tracking their master branches is to remove the submodule and add it back every time when cloning the super project.