Dalang, Ah, my favorite subject. I read your issues and they certainly sound like something isn’t right. If Project isn’t prioritizing properly against task priorities, make sure you have your leveling order set to Priority/Standard (Resource tab, Leveling options). I can’t answer your issues with over-allocation as this goes beyond what Project will do, but I’m sure there’s an answer. Question, are the task units set no higher than the resource max units?
Start with that and let me know what you come up with. Worst case I can take a look at your project if you want. I’m sure there’s an answer.