Inspector doesn't show public variables of subclass of a class that inherits from MonoBehavior?

I’m not sure if Unity doesn’t supports this or if I’m doing something wrong.

There is a class that is a MonoBehaviour in an Asset Store asset.
I want to extend it to add functionality, so I did.

However, the inspector doesn’t seem to be showing the public variables I define on the extended class. Is this normal? If so, then how would I make it also show the public variables for editing?

Actually, I found the reason. It was because the parent class had a custom editor assigned.