submodule add -f errs on un-ignored path

git submodule add tells me to use -f because the path is ignored in 
gitconfig (even though I un-ignored it in .git/info/exclude), but with -f it 
give usage error.  (git 1.7.1)  Is this rejection by git intentional or 
unexpected?  (This is my first foray into submodules.)

/etc/gitconfig is set to excludesfile that ignores:  "WebPortal/Images/" 
entry

local .git/info/exclude is set to un-ignore it:
cat .git/info/exclude
!WebPortal/Images/
!WebPortal/Images
!WebPortal\/Images\/
!WebPortal\/Images
!WebPortal\/Images/

$ git submodule add file:///home/me/super/Images.git WebPortal/Images
Adding existing repo at 'WebPortal/Images' to the index
The following paths are ignored by one of your .gitignore files:
WebPortal/Images
Use -f if you really want to add them.
fatal: no files added
Failed to add submodule 'WebPortal/Images'
$ git submodule add -f file:///home/me/super/Images.git WebPortal/Images
Usage: git submodule [--quiet] add [-b branch] [--reference <repository>] 
[--] <
repository> [<path>]
   or: git submodule [--quiet] status [--cached] [--recursive] [--] 
[<path>...]
   or: git submodule [--quiet] init [--] [<path>...]
   or: git submodule [--quiet] update [--init] [-N|--no-fetch] [--rebase] 
[--ref
erence <repository>] [--merge] [--recursive] [--] [<path>...]
   or: git submodule [--quiet] summary [--cached|--files] [--summary-limit 
<n>]
[commit] [--] [<path>...]
   or: git submodule [--quiet] foreach [--recursive] <command>
   or: git submodule [--quiet] sync [--] [<path>...]

v/r,
neal