I can reproduce the bug in the latest master. On a Windows machine,
and starting with emacs -Q, I do:
M-x customize-option RET tutorial-directory
and try to complete with C-M-i inside the editable-field, with different names,
and different cases.
It doesn't work, because the completion is made case sensitive, even though
read-file-name-completion-ignore-case is t.
Also, the completion is made not only for directory names,
but also for file names. This also happens on a GNU/Linux machine.
Since the 'file widget suffers from the first mentioned bug as well,
the attached patch tries to improve the completion for both of these widgets.
Best regards,
Mauro.
0001-Improve-file-name-completion-in-file-and-directory-w.patch