Well... that's rather confusing.
If you use the ticked value in any way, it changes the font face for some reason. I even tried storing the ticked value as a global var, rounded it, converted it to int and it still changes the font face. I have honestly no idea why it's doing that. And it appears to only be doing it for the value returned by the plugin. I set the text size manually and it worked as intended.
But I did find a workaround.
In the line where you set the START_TEXT font size to the ticked value, add a line below it.
-> START_TEXT: Set font face to "Arial" (normal)