That's completely normal for a coin launch where there is a ton of hashing power trying to mine while difficulty is extremely low.  Nothing nefarious happened.  That is how it works.  All the screaming, whining, and gnashing of teeth was done by those who don't have a basic understanding of how coins work. 

The coins you thought you mined were orphaned.  You and someone else mined those same blocks at the exact same time.  They submitted them before you did, and they got credit for them and you did not.  That's how the cookie crumbles.  The same thing happened to me.  300+ transactions and they all disappeared once difficulty rose and the blockchain caught up.