I believe some exchanges gain interest on the zeitcoins they hold for others and then sell to make a profit. (Even though they all denied doing such a thing , odds are some are.)
I would recommend the Zeitcoin Dev make an update that increases the rate at which the interest rate decreases instead of yearly to either monthly or directly to the final rate to help save the coin from bad behavior by some exchanges.
Just My 2 Zeitcoins:
Even the PoS coins at 2% are taking a pummelling from the cetaceans