How to split into two pages two aliases?

Hi All,

I know that there is the possibility to merge duplicate pages buy default and with plug ins.
I have the opposite issue I have a page A with some aliases B, C, D.

Down on the road I understood that C (for example) is to properly an alias and it would need its proper page. So I removed the alias C in the page A and I created a new page C with different aliases x,y,z

But What happened is that both page A and page C now have the same aliases B,C,D,x,y,z and themselves. the funny thing is that when i try to edit the aliasese seem to be not actually written.

Anyone has any idea how to solve this?