git add after changing a submodule

If I make a change to a submodule and commit it, I then have to add it to the parent repo. If I do

git add path/to/submodule

then it works fine.  But if I do

git add path/to/submodule/ (with trailing slash)

then it blows away the submodule and adds all the files in that directory.

Seems pretty dangerous to me. I know that I can just use git commit -a to do it, but I'd like to prevent the mistake of adding the path and screwing up the repo. Is it possible to protect the submodules a bit more?

Pat