As you've discovered, any formatting applied to the text inside the field will supersede the formatting applied to the field object while in layout mode. Once you start formatting text inside the field, you'll need to use the text format bar to control the text format for that field in that record. Thus, if you want to format additional text in the field to match the original format specified for the field, you'll need to do that manually when you enter/edit the data.
Oh my....I was afraid of that! I guess I'll just go with unformatted text! Thanks for the speedy reply!
For those reading this thread, here's an auto-enter calculation that will strip all formatting out of text after it is entered/pasted. It's a very useful function on Mac systems where formatted text may be pasted into a text field:
TextFormatRemove ( Self )
And clear the do not replace existing value checkbox.