Voodoo - trying to edit system text size

Yeah, that's what it's supposed to do.

If you want to change the properties of the text in a System Text field, double-click the field (which will select all the text or give you an edit cursor), select the part of the text you want to change (anything from all of it to one character, or even none if you want NEW text to have the new property), and go to the Properties tab (upper left). Here you can select (under Text) the font, style, size, horizontal and vertical alignment, special characters, (and under Show More) whether it scales with the staff or not, borders, line spacing, text style, and position.