If the MODE is changed, then set the submode to an empty string.

pyqso/record_dialog.py

@@ -273,9 +273,10 @@ class RecordDialog:
     def on_mode_changed(self, combo):
         """ If the MODE field has changed its value, then fill the SUBMODE field with all the available SUBMODE options for that new MODE. """
         self.sources["SUBMODE"].get_model().clear()
-        text = combo.get_active_text()
-        for submode in MODES[text]:
+        mode = combo.get_active_text()
+        for submode in MODES[mode]:
             self.sources["SUBMODE"].append_text(submode)
+        self.sources["SUBMODE"].set_active(MODES[mode].index(""))  # Set the submode to an empty string.
         return
 
     def on_key_release(self, widget, event):