There have been special star upgrades for the main castle in the past. So it is not a bug that the resent upgrades do not work in the main castle. I think a lot of players don't need main castle star upgrades anymore. Possibly the resent upgrades can be adjusted so that they can be used in all castles?

Also, it would be usefull to be able to choose the kind of resources you want to upgrade.
Now it automatically upgrades the kind of resources with the lowest stars.

When you have 4/4/4 stars and want to upgrade your ore to 5 stars, you will have to upgrade stone and wood first, because they will automatically be chosen.

Quote from LastSamurai

Also, it would be usefull to be able to choose the kind of resources you want to upgrade.
Now it automatically upgrades the kind of resources with the lowest stars.

When you have 4/4/4 stars and want to upgrade your ore to 5 stars, you will have to upgrade stone and wood first, because they will automatically be chosen.

Totally agree, it would be great if the increase in stars can be used in all castles without distinction and that you can choose what material you want to increase in.

As far as I know, the added stars that are still in the game only work in normal castles. Not in the main castle, not in event castles (mage, gold, ghost ect) and not in amber castles. Is it possible to change this so that they can be used in all castles or is it possible to develop additional stars stars for the other castles? I turned an event castle into an amber castle and would like to add extra stars to it.