[Freesurfer] Zen of label editing in tksurfer

Folks:

We notice that when we try editing labels in tksurfer (eg: draw an outline, fill with new label value), this results in tksurfer's control panel showing two labels everywhere (even where we didn't edit), with the second one saying "1 additional label" (or something like that... don't have it running at the moment).

Further exploration has us puzzled about deletion, saving and so on.

What is the model that tksurfer is following here?

If you load one label file, and then start editing, is that like tksurfer introduces another "layer" (ie: a second label slot for every vertex?). How do you load a label file and explicitly edit that data instead of creating new data?

Thanks,

Graham