Create a Label, use setJustificationType( Justification::centred ), and allow editing.
Result: The label text is centered, but when the user clicks to edit the label, the resulting text editor is left justified, causing the text to jump to the left.
It would be desirable if, when entering edit mode, the text editor activated in such a way that the text did not visibly shift at all, to create the appearance that it is being changed in-place (i.e. displaying using the Label’s Justification).
In addition, if a Label is editable, but the editor is not active, the cursor should probably change to an I-beam to indicate that the text can be edited. And if you want to provide the option to pass the click that activated edit mode, on to the text editor, so that the insertion point can be set to the place where the user clicked to get into edit mode, hey I’m not going to hold that against you (but if you don’t do it, I won’t complain either).