So - I tried a new game today. I have the same Problems with the Druid, als the Cleric. 16 Slots to prepare (although I dont even have so many spells)...Switched every addon off... and have no idea, why the problem still persists. I added two addons (the hair meshup and the druid gear) into the data folder. Could there something be, that broke it?
One thing I noticed:
When I start a new game, everything in the chests stays the same. No matter, which char I have. Normally the things in the chests change. But not any more...