See bug #614006 for the background behind this bug.

1. Go to a folder in a terminal.
2. Do this:

file="1"
while true; do
    touch $file;
    file=$(($file + 1));
    sleep 2;
done

3. Visit that folder in the file chooser.
4. Hit "Create folder"
5. Start typing a name

You will see that when a new file gets created, your typing will be cancelled.

The file chooser should still let you type your new folder's name even when the file system model changes.