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.