We always work with FLAC files, but I don't know if that makes any difference. I'd appreciate some clarification on this topic, though.
In the Tools > Options > Tag Panel window, there is the ability to edit characteristics of each field appearing in the Tag Panel. You can create and name a field and you can give it a user-friendly name that appears above the field window, but I do not understand why there is an option for the "default value" of a field. Isn't the field's value supposed to be blank if there is no value for that field? If multiple tracks are selected and that field has different values in those tracks, isn't the field's value supposed to be "keep"? Why would anyone choose "blank" or "enter"? Why is there a need to provide this option, and what should one choose for normal operation?