Hero Splitting

I've encountered this situation three times in my gameplay. It usually happens when there are more than 8 heroes. A hero from the garrison is cloned within the castle. I was able to resolve it in the following way: I moved the clone out of the castle by a few steps and then dismissed him. After that, the second copy exits the garrison and enters the castle, and I can control it. If I don't do this and start exchanging troops between the clones or combining them, I lose control over another one of my heroes.