Im not sure how to explain it so I'll just out an example.
Say your castle has 20 space. So you ask for a dragon.
Someone donates 5 archers.. leaving you with 15 space.
So you delete the 5 archers.
on your map you will see now 20 space available.
BUT in the chat menu, where people can donate to you, it will still be 15.
get it?





