this behaviour is expected and will remain in future versions of Workshop. All 5-point scales are valued as 0, 1, 2, 3, 4 everywhere in Moodle. The only exception is with the sum aggregation method, where such scale would be valued as 1, 2, 3, 4, 5 (with 0 meanings "no rating given"). See http://docs.moodle.org/en/Scales#Example_scales for more examples.
Unfortunatelly, current version of Workshop does not allow using custom scales. In Workshop 2.0, you will be able to use your own scales (from those defined in the course or the site) so you'll be able to modify the scale to fit your needs better.
Hope this explains although does not help too much...