Unable to add textFrame to a cell by scripting

Using extendscript I want to insert a textFrame at the end of a table cell that contains several paragraphs. But this keeps throwing an error stating that this is not allowed for graphic type cells. But the cell is not a graphic type, as I already placed several paragraphs in it. And even after forcing the cell type to text the error remains:

        cell.cellType = CellTypeEnum.TEXT_TYPE_CELL;

        newFrame = cell.textFrames.add();

Throws a runtime error as indicated.

Is this a bug ?

Running version 21.4.1.164