tkMessagebox.askyesno always returns False

[peter]

I've managed to narrow down the circimstances in which the error
occurs.

The application is a file manager (not terribly original,I know, but my
main purpose is to gain experience in using Tkinter).  It displays the
contents of a directory in a list box, and then applies the function
(in this case rename) to the selected items.  There is also a secondary
list, named tag_list, which can be loaded from disc and used to
preselect files.  If I call the function filter_taglist once, it
behaves itself but after I load a differenct tag list and repeat, then
the confirm dialog always returns False and the action fails.

I'm baffled!!!!

Code snippets below show
 1.  Loading the tag file from disc
 2.  Matching the tag file to the main file list
 3.  Renaming all selected files

(comments starting ## have been added in this post)

<code>

    # Load from file
    def load_taglist(self,ask_file_name=1):

        #if ask_file_name  get tagfile name
        if ask_file_name:
            a=fd.askopenfilename(title='Tag
File',initialdir=os.path.split(self.tagfile)[0],filetypes=[('Tagfiles','*.tag'),('All
files','*')])
            if a=='':
                return
            self.tagfile=a
        ## entTag is an entry bix which shows the name of the current
tag file
        self.entTag.delete(0,tk.END)
        self.entTag.insert(0,os.path.split(self.tagfile)[1])

        # read file
        self.taglist=[]
        try:
            fp=file(self.tagfile,'r')
            while 1:
                a=pstring(fp.readline())
                if a.text=='': break
                a.stripcrlf()
                self.taglist.append(a.text)
            fp.close()
        except:
            mb.showerror(self.tagfile,'Error reading from tag file')
        self.show_taglist()
</code>

<code>

    ## This function reads every file in the list box and checks it
against the tag list
    def filter_taglist(self):
        for i in range(self.lstFiles.size()):
            f=self.lstFiles.get(i)
            if f in self.taglist:
                self.lstFiles.select_set(i)
                self.lstFiles.see(i)


</code>

<code>

    ## This function applies a user specified function to each selected
file
    def file_control(self,action):

        ## set up list of files - element 0 is the path and elements 1
up are the files
        ## get_listbox_contents(1) is a function which returns a list
of
        ## listbox selected contents (instead of just their position
number)

file_list=[self.file_path,]+widget(self.lstFiles).get_listbox_contents(1)
        exit_flag=0
        file_count=len(file_list)-1
        if file_count==0:
            mb.showwarning(self.title,action+': No files selected')
            return

        # Initial conditions. If the user cancels, or the conditions
are insufficient,
        # set an escape flag

        if action=='Rename':
            i=mb.askyesno(file_list[0],'Ok to rename %d selected
file(s)' % file_count)
            if i==0: exit_flag=1

        ## etc
<code>