Shadowcraft bases its decisions on your current stats. Its entirely possible that doing something it suggests flips the values. Assuming you haven't discovered a bug, if you hit the reforge button again, it should have reforged back (or to something else higher).
If you're dummy testing, I hope you are not sub and using the raid buff dummy with sessions of 1 hour of your optimal level of play minimum or its near worthless. Theres a reason simcraft runs thousands of iterations. 1 5 minute test, sim or actual, isn't likely to give you enough information to be useful... in fact if it did, you could probably have eyeballed the choice if you knew the mechanics well enough.
I think you are trying to say mastery is better if you are off the target more because it is ticking. Expertise is also really good if you are getting off target a lot though. If you are off even a relatively short time you will energy cap and at that point having your stuff dodged is wasting energy and also delaying combo points if you need to refresh something. If you have been off a while or are opening, having stuff dodged will significantly increase your ramp up, such as having your mut dodged preventing applying rupture or SnD. Again its about variance.