Technically, the recalculation works. But the feature editing interface is not very user friendly at the moment.

We plan to improve this. Until then, here's the trick:

You will need to double-click on the feature (polygon or line) so that the "bubble" pops up. With the bubble open, make changes to the polygon or line. You should see it immediately recalculate. When you are done, hit save on the bubble, and then "Save features."

More information is available here:

http://community.mylandplan.org/mylandplan/topics/problem_with_editing_f...