If you use a screen's onLoad method to set a numeric field to a special missing character (.A, .B, .C,...,.Z), it will not appear to work. If you commit the record, the value will be there. Any of the normal methods to update the screen will not work such as field._refresh(); or field._update();

The following will work:

field.text=field.text;

where field is the name of the variable on the data set/screen.