Create a new notebook with the following two input cells:
NotebookWrite[EvaluationNotebook[], Cell[BoxData[ToBoxes[Manipulator[Dynamic[x]]]], "Output"]]
and
y = 10 (* dummy cell *)
If you evaluate the whole notebook (Evaluation menu\Evaluate Notebook
), you will see the manipulator appear then quickly disappear.
If you manually evaluate the first cell, the manipulator will not disappear.
Why is this happening?