Multiple Keybase accounts proves with the same Twitter account?

I'm not really sure if this is an issue or designed so by intent, but right now I actually have two Keybase.io accounts, which share identity proofs of one Twitter account:
[boegh](https://keybase.io/boegh) (person a) and [heb](https://keybase.io/heb) (person b) both have proofed their identity with [twitter.com/boegh](https://twitter.com/boegh).

This can be either by intent; i.e. multiple users linking to an organizations Twitter-account (sort of the opposite of #330). It can also be that nobody thought of it, in which case it may be an issue (I haven't found this discussed among the issues), in case person b hijack person a's Twitter acount.

It makes me wonder though, if the first person (person a) to register a proof with a Twitter account, should receive an e-mail or something if another person (person b) tries to register a proof, with a Twitter account, that is already registered in Keybase?

Start by reviewing the issue's existing identity-proof registration flow and the related discussion in #330. The issue does not name files or tests; first determine whether duplicate Twitter proofs are intended, then define the expected behavior for an already-registered account and how completion would be verified.

Written by the indexing model from the issue text.