I realize that this might not be your area, but hoping that you have seen this before and found a solution.
Using the JCE Editor, type in the text, highlight it and click on text align, center or even right and nothing. It apparently won't center anything I.e. tables or text.
Reading other forums, someone thought that it was their template css file that over wrote JCE, but since you are still in the editor, that doesn't make sense.
I am getting around it with align="center" added to the code. BUT a PITA.