Git Accuses Ignored Directory Has Modified Content

I have the content directory in my .gitignore file, as follows:

app/dir/*

But when I give git status , git says the following:

# On branch master
# Changes not staged for commit:
#   (use "git add <file>..." to update what will be committed)
#   (use "git checkout -- <file>..." to discard changes in working directory)
#   (commit or discard the untracked or modified content in submodules)
#
#   modified:   app/dir (modified content, untracked content)
#
no changes added to commit (use "git add" and/or "git commit -a")

In my understanding, he should not even know or call if there is any modified content within that directory, since it should be ignored. What does this status mean, and how to solve it?