Steps to Reproduce:

1 Start Emacs clean

/Applications/Emacs.app/Contents/MacOS/Emacs -Q
1.1 Note: Emacs Version

emacs-version is a variable defined in `C source code'.
Its value is "24.0.94.1"
2 Load Org Mode and some sample tags

Evaluate the following in the scratch buffer

(require 'org-install)
(setq org-tag-alist (quote (
                            ("tag_a" . ?a)
                            ("tag_b" . ?b))))
3 Open the following org-mode file

* Header 1
** Header 1.1
* Header 2                                                                      :Personal:
4 Point should be on the first asterisk for “Header 1”

5 Type C-c C-q to bring up Tag selection

The expected result is the fast tag selection; this works

6 Type <TAB> to enter free tag selection

The expected result is that the Minibuffer prompts with Tag:; this works

7 Type Per followed by <TAB>

The expected result is a completion of the file-tag Personal; this works

8 Type tag_ followed by <TAB>

The expected result is a completion list of tag_a and tag_b, this does not work and the Minibuffer prompts [No match]

Note that if I were to remove the single characters for tag_a and tag_b completion works for those two but not for the Personal tag from the file

Shouldn't free tag entry always show all possible tags, regardless of the setting of or use of fast tag completion?