(Posted to StackExchange a week ago, with no response.)

I have used the Option Inspector to set CellGrouping to Manual for the current, selected Notebook. Nonetheless, the following does not group these two cells together:

CellPrint[CellGroup[{TextCell["hello"], TextCell["goodbye"]}]]

Also, adding the second argument to CellGroup[] to specify which cell should be open, does not work.

Please note that both of these work if I create the cells in a new Notebook, created with CellGrouping -> Manual.

I saw the same behavior with Cell[CellGroupData[...]].

What am I missing?