Hello,
I've got several addresses in my blockchain.info account. I decided to import them into Electrum. I used the private key from bc.i for address 1xxxx.... but when I imported it, the resulting address showed 1yyyy... It was completely different! I even re-imported the same private key back into bc.i and it too imported a completely different address (same address that Electrum showed).

What the heck happened? Can I no longer use those older addresses? Some are vanity with custom prefix that I'd like to keep using.

Yes, they are all at least 2-4 years old. Did some calculation standard change recently?

Thanks!