Recipe switch from Extract to Partial Mash - ABV change for specialty grain?

I entered the following recipe that I found for a hoppy red ale as an extract recipe:

2.0 oz black barley (500.0 SRM)
8.0 oz Caramel/Crystal Malt (60.0 SRM)
1lb Carared (20.0 SRM)
6lbs Amber liquid extract (12.5 SRM)
+ hops (amarillo, centennial) and WLP001 yeast

When I entered the recipe for the purpose of a 5 gallon extract brew, the ABV and OG was at the low extreme on the gauge (3.7% and 1.037) and the bitterness at the high extreme (59.0).

Just for fun I wanted to see what the calculation would be if I switched the type to a partial mash. The values then looked normal (OG 1.051 and ABV 5.1%).

If I am only using specialty grain yielding non-fermentables in the steeping process, how is my ABV changing from extract to partial mashing?

This is only my second batch, please enlighten me.

Hi,
  If you want to send the recipe along I can take a look at it.  Note that the ABV may change a bit depending on ingredients.  BeerSmith tries to match OG, color and bitterness levels when converting but for a variety of reasons any conversion can't be entirely perfect.

Brad