git-add creates broken submodules

Hi there,
with help of doener (#git on freenode) I found
the root cause of a misconfigured git repository
being in the way 'git add <path>' behaves when 
<path> contains a .git repository.

Example:
$ (mkdir foo; cd foo; git init; git commit --allow-empty -m ini); \
  git add foo
$ git submodule status
No submodule mapping found in .gitmodules for path 'foo'

Such commit ended up in our centralized repository so that all
clones now have this 'submodule' w/out entries in .gitmodules
and .git/config.

Should 'git-add' simply consider any .git as a normal entry
instead ? (that's what I'd expect) 
Or, if not, should it warn about the presence of
a .git directory and refuse to continue suggesting
'git submodule add' instead.

NOTE: this happens with git version 1.6.0.2


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