Water volume problem on brew steps

I'm having problems with a brew in BeerSmith 2.1. 

When I have the mash option 'Drain mash tun' checked, I get 7.41gal strike + 3.70gal sparge for an estimated pre-boil volume of 8.49.



When I have that option unchecked, I get 7.41 + 4.37 = 8.49.  An extra 0.67gal of sparge water but not an increase in pre-boil volume.



I've attached a copy of my recipe.

Out of curiosity what is your dead space set to?

When you uncheck drain mash tun is it also unchecking adjust mash vol for deadspace?

My deadspace is set to 0.25 gal.  And no, when I check that box, the 'Adjust mash volume for deadspace' does not change.

OK, I thought maybe the difference was dead space. Well, I'm out of ideas!  ;D

This is a total SWAG, but maybe the drain/no drain check box is telling BSmith you intend to completely drain the MLT dry, thus advising you to use 0.67 gallons more for sparge performance to ensure grain bed gets fully soaked again. 

The pre-boil volume is determined elsewhere and would not change based on how one batched, so the extra 0.67 is solely used to flood the MLT but not expected to reach the boiler. 

I am seeing this same problem, running Beersmith 2.1 on OS X. Problem seems to occur when there is a double-comma thing ("Drain mash tun, , 3.7 gallons...") going on in the steps.