When using the widget with only short form SetText attributes (field="value) -- the default field (text) of the default tiddler is set to the default value ("") -- thus clearing the text field of the current tiddler. I have inserted a conditional to test for the presence of the `field` attribute.
Whilst I was about this, I have inserted code to enable the setting of any number of TextReferences -- this fixes the issue of only being able to set one index per widget and also allows different tiddlers to be targeted by the same widget.