Other address you are transferring the whole bitcoin address if you install the private key in other wallet provider?
I just try this when i was installing the private key in the same wallet in electrum only one address is you can get..
Unless if you are using 2fa in electrum when you are backuping private key you can get different address.. when installing it to other wallet or in same electrum or wallet..
Sorry, but i can't really understand your question... I think you're saying that you can not import a private key into an existing electrum wallet.
This is partly correct.
You either generate an HD wallet, this wallet uses a seed in order to generate an xprv. This xprv is used to generate a bunch of derived addresses.
Once you used electrum to generate a HD wallet, you can no longer use this wallet to import private keys, since theys imported keys could not be derived from the wallet's xprv.
But, if you generate a new wallet in which you restore the wallet from a private key, the resulting wallet won't be HD. Since the wallet isn't HD, you can import extra private keys.
Long story short: if you want to import private keys into electrum, make sure you generate a wallet that isn't generated from a seed, but from a private key... Once you have a wallet that is generated using a private key, you can add extra private keys to it.