I've spent way too much time on this. The text inside a text box is scaled by 200%. I can see it when I use the text tool to click on the text and the percentage shows up in the Info Panel. Mind you the text box is at 100%. The result of this is that when I copy the text and place it in a new text box it defaults back down to 100%, making everything smaller; 50% of what I copied it as. I have to adjust it every time. This is just a mild inconvenience, but I would love to know why this is happening. Thanks for your insight!
I was able to repeat your issue - you must have enlarged the text with a transformation. To undo it - do a select all with the move tool and in the properties panel, type in 50% - Then it should go back to 100% in the info. Resize your text i the character panel - don't transform.