No one is taking your money. Once it is in your wallet that is yours and no one has the power (without extremely drastic measures, i.e. hard fork ) to touch that. But in-progress post rewards are always subject to change due to changing votes, market prices, changes to other post earnings, etc. People can add votes, remove votes, add downvotes/flags, all of which change the post reward amount. Until it is paid out, it is still part of the Steem reward pool, and not your money, yet.