First of all: welcome to the forum
@Andarien and congratulations for your first post !!!

I am very sorry for stupid question, especially if it was already asked...
there are no stupid questions!!
But do I put ghosts on an open HAUNTED cemetery when a tile with ghosts enters play?
No.
Haunted cemetaries (as from level 5) do not at all work like normal cemetaries (level 3 and 4).
The only ghosts you have to place is when you draw the tile with the cemetary. At this moment you have to place 1 ghost on each adjoining tile showing ghosts.
But seems like everyone else thinks that normal cemetery rule does not apply on haunted one.
yes, everybody else is correct

But does it not make it weaker? I feared it mainly because it sped up the ghost infestation so much. Without the basic rule it does not do that. The "haunted cemetery enter into play" ghosts are easy to avoid if you place it somewhere where is no mist. So it just eats the tiles. Which is not the end of the world. Should the last stages not be the hardest?
Exactly, the cemetary eats tiles because in each turn, at the end of each turn, you have to place an additional tile upside down.
This speeds up the game and makes you reach the bottom of the current pile of tiles much earlier - and as soon as you are out of tiles in the current pile of tiles you lost the game!
In addition, the rules concerning upside down tiles prevent features from being completed so you cannot score so many points and meeples can get trapped.
In my personal experience, the haunted cemetary is a real pain (because of the 2 tiles per turn)! So maybe check the checklists to see if there are other rules which you do not apply correctly.
Let us know if you found something!

And if not: well done with your management of hounted cemetaries!!
