Problem occured with same name of cluster in different machines


I have a weird issue today and it gives me lots of problem. I had two cluster different but unfortunatelly I gave them the same names by mistake;

lets say;

both cluster have had totaly different machines ( it was working well its been one month)
today I added a machine in one of the cluster and I saw that all the machines were in the same cluster physically (it was not the case before adding the machine)
I have chacked the unicast list; there were no machine in common
So someone can explain me how I had this problem and how I can seperate them ?

Thank you

This is why -

Your best option is to use and then move indices to their correct node, then shutdown one cluster and change the cluster name.