You must have some very young coins and not too many of them. 50% interest per annum is still 50% of your coins per annum.
If you had 100DMDs in your wallet, closed the wallet and opened it one year later you would mint 50DMDs. 
The tooltip info is... not something you should rely on. There is no way of saying  when you would mint, it's as luck based as Proof of Work mining.

Besides, {"proof-of-stake" : 0.15827990} difficulty is very hight at the moment and now I've opened my wallet to mint my 2 week old coins - behold