Updating the font size drop-downs in the main window and the tag editor was being handled manually and had some odd behavior such as point sizes changing to 10 when selected, preventing that size from ever being selected again. Changing the combo box to follow Qt's model/view approach seems to have addressed much of this.
The handling of the (Default) label in the combo box was changed to agree with the MVC pattern and completely by accident made the appearance more consistent with the other fields in the tag editor that have default values. Qt's default Font() assigns a default size by pixel on Linux, so no default point size is available, so a reasonable default of 10 points was chosen.