guix:
There is no decimal point in the SevenSegNumFont. Here is your problem! And you can't just add it like the space character was added. I'm (slowly) working on rewriting the font loading code of the UTFT library.. Hard task, for me anyway
Why are you doing this??? UTFTs printNumF() already has everything you need. Use the SevenSegNumFontPlus font and add a blank character at the end. Change the ':' to a '.' if you want to. Then simply specify ':' as a divider and ';' as filler. There is no need whatsoever to rewrite the function for this.
Font can he downloaded here: Electronics - Henning Karlsen
/Henning