Boil addition affecting pre-boil gravity

On a whim I decided to add 1/2 pound of maltodextrin to the boil kettle yesterday.  When I plugged it into my recipe as a 15 minute boil addition, I notice the Estimated Pre-Boil Gravity number jumped.  What gives?

BeerSmith totals up all fermentables (anything in the Grain database) for both pre and post boil, regardless of when they're added. This includes sugars added at intervals during fermentation.

This simplifies the math associated with boiloff, alcohol potential and estimated final gravity.

That is an interesting approach.  I will have to remember to note the estimated pre-boil gravity before entering any boil additions in the future.  Or at least zero them out momentarily.