A subtle point about resetting a paper account is that, in actuality, one is creating an entire new account. Moreover, the old account is still there. So, the previous keys still point to the previous account. The account is ‘inactive’ which is why the keys don’t validate for fetching data. However, all the account data, orders, etc are still there. Not sure I would go so far as to call this a ‘feature’ though if for some reason one wanted to look at old paper account info it’s there.
I do agree it would be nice to copy the keys to the new ‘reset’ account just like name etc are copied. (It would save a lot of support requests for sure) However, the secret key is, how should I say, secret. For security reasons it isn’t really stored anywhere. The only way to get a matching secret key is to regenerate it.
I will however add this as a request to our issue tracker. Maybe others will have ideas on how to implement something better?