This behavior can manifest if a GUIDE FIG-file is copied to create a new GUI. When the new FIG-file is opened in GUIDE, the callback properties of the GUI components still point to the old GUI program file. Therefore, if a new component is added, its callbacks will not be automatically created in the GUI program file and attempts to view the callback functions will be unsuccessful.
To correctly copy an existing GUI to a new GUI, open it up in GUIDE and choose "File > Save As". This will create a new GUI program file and modify all the callbacks of the GUI components.
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