Inconsistent font sizes on Keynote

I'm trying to make the font sizes consistent over multiple textboxes on one slide, but the text that is supposed to be the same size is oddly not. For example, 18 pt in one box is clearly bigger than 18 pt in another box (and I've triple checked that I've entered the same number for each box). It's as if the text is being automatically scaled in size to be relative to the different sized textboxes, despite the font size number. Is there a way I can "fix" the font size so it doesn't scale within the textbox?