IBUs Increase as boil time is added

I am running BS 2.0.48 on windows 7 64 bit.  this issue is also present on the last build and updated to the newest build before posting this bug report.
When I increase the value for Boil Time it increases my IBUs estimate. My first hop addition is set to 60 minutes (only one hop addition for this recipe).
Shouldn't the estimated IBUs be unaffected by the boil time? The hops are still added with 60 minutes left in the boil

One variable in the utilization formulas is wort gravity.  Even though boil time is fixed at 60, the gravity of the wort changes during the entire boil. 

If you tell BeerSmith you're boiling for 90 minutes (versus 60), then BeerSmith is likely estimating wort gravity differently.  With a longer boil, you get more "gravity" from evaporation of water and concentration of the sugars, and so need less PPG from the grains, meaning the average gravity during the entire boil time has shifted slightly lower, and utilization generally increases with lower gravity worts. 

This is one reason recipes with simple sugars often say to add the sugar toward the end of the boil so as not to impede utilization by boosting the gravity. 

@maltlicker : you're right but Beersmith doesn't adjust gravity after boil when you increase the boil duration (which could appear kind of strange), so utilization may not change...

I agree that logically, increasing the boil duration would result in a lower gravity after boil and increased bitterness but it's not... for the moment  :

Jean-Luc said:

@maltlicker : you're right but Beersmith doesn't adjust gravity after boil when you increase the boil duration (which could appear kind of strange), so utilization may not change...

I agree that logically, increasing the boil duration would result in a lower gravity after boil and increased bitterness but it's not... for the moment  :

Click to expand...

Not sure what you mean by "after boil." 

I played with boil times and hop drops, and got the changes I described.  But, the changes were minimal, as in under 2.0 IBUs.