This is not a bug this is how it works. The font size is adapted to the width of the text area.
Can you provide an image of how you want the result to look like?
Maybe "bug" wasn't the correct term.
I made the attached pic using "single lines" of "add text" as opposed to using "add text" and being able to use return and type in another line.....
Need it so that customers can type in say 4 lines of text and that each line justifies to width as the look in the attached pic.
This is currently not possible. If this is an option you need you can hire us via www.fancyproductdesigner.com/customization-request to code it for you.