Lukas, The associated merge request failed unit testing. Mind taking a look?
Patrick, you need to fix this with another patch: https://github.com/theforeman/foreman/pull/5142 - not related.
VERIFIED on sat6.3.4-1 - the default old behaviour is back: i was able to re-discover the host despite the fact that i had it in the managed hosts. switching the mentioned setting to TRUE (to error out) indeed prevents the same host from being discovered again (the /facts POST requests receives 422 with a proper message)
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHBA-2018:2915