progress bar is not updated despite "uses threaded animation to true"

I have implemented a progress bar and text field in my app copying Progress indicator not showing up immediately. Please look at the code below.


                        tell progress indicator "BarberPole" of window "ImgFuserWindow"
                                -- This makes the application use a separate thread to handle the animation
                                set uses threaded animation to true
                                set indeterminate to true
                                set visible to true
                                start
                        end tell
                        set content of text field "ProgressText" of window "ImgFuserWindow" to "Some text"
                        set visible of text field "ProgressText" of window "ImgFuserWindow" to true
                        set AISTool to quoted form of ((resource path of main bundle) & "/align_image_stack")
                        do shell script AISTool & " -a fused " & " " & ImageList
                        stop progress indicator "BarberPole" of window "ImgFuserWindow"
                        set visible of progress indicator "BarberPole" of window "ImgFuserWindow" to false
                        set visible of text field "ProgressText" of window "ImgFuserWindow" to false

ImgFuserWindow is my main window. I reserved a “corner” of the window, with the hidden text field and the bar, to display progress when necessary.
Maybe I could use a popup progress window, but I prefer to do it like this.

However, both the progress bar and text are not shown onto the screen. At the end of the shell run the text field and bar it sometimes appear to immediately disappear again due to the visible=> false setting.

Can someone please tell me what I do wrong?

I have already resolved it in using a separate window. However I am still very much interested in a fluently running version inside the main window.