do nothing if dropPos == idx

since such move won't change the field position
and when trying to move the field below itself
may lead to it being moved below the next field

qt/aqt/fields.py

@@ -60,6 +60,8 @@ class FieldDialog(QDialog):
         indicatorPos = fieldList.dropIndicatorPosition()
         dropPos = fieldList.indexAt(ev.pos()).row()
         idx = self.currentIdx
+        if dropPos == idx:
+            return
         if indicatorPos == QAbstractItemView.OnViewport:  # to bottom.
             movePos = fieldList.count() - 1
         elif indicatorPos == QAbstractItemView.AboveItem: