Invalidation of keys that require fingerprint authentication (on each use)

[Android Central Question]

Referring to a documentation where it's stated;

... Such keys can only be generated or imported if at least one fingerprint is enrolled (see FingerprintManager.hasEnrolledFingerprints). These keys become permanently invalidated once a new fingerprint is enrolled or all fingerprints are unenrolled.

I get that keys are permanently invalidated when all the enrolled fingerprints get unenrolled but why it is so when there's a new fingerprint enrolled?

I thought Android Keystore abstracts the key usage from the fingerprints enrolled (when "authentication-required" set on a key) which would mean I can access the key(s) that require authentication defined by my application, regardless which enrolled fingerprint is used.

So, would that mean my keys will not be usable anymore once I enrol another fingerprint? Or I'm interpreting that statement (in bold) very wrongly?

 

[Rukbat]

No, you're not, and yes, they will be unusable.

Why? Because that's what Google chose to do to enhance security. If I get your password or pin (and that's easy with binoculars), I can add my fingerprint to make it easier for me (after I've stolen your phone). And I'd be able to do all sorts of stuff from that point on.