User blog comment:Omega natsu2/Chapter 357: The Nine Demon Gates, Predictions./@comment-5409550-20131020040405/@comment-4829046-20131023121929

Or they find out that it actually cancelled their Dragon Force or at least suppressed it and now have to undergo some power-up/training/battle that allows them to unlock it again. Remember that Dragon abilities are apparently different according to your level, where the other DS(Gajeel shown) gained motion sickness only after a major power-up. But perhaps I'm reading too much into this :/