I "investigate"

grep sub\s+might_have

grep sub\s+add_relationship

grep relationship_data

grep relationships

$self->_relationships(\%rels);

$new->{_relationships} = { %{$new->{_relationships}||{}} };
my $rel_names = $self->result_source->{_relationships};

  _relationships  => {}, # copying them as-is is bad taste
[download]

So there doesn't appear remove_relationships

Every object and its mother (row and source) appears to get/carry a list of _relationships

which is just a hash ref accessed/modified using _relationships

So if you're trying to modify it, but its being cached, you need to modify the other thing (resultsource...whatever)

If you post a simple test case, code I can run, say something that depends on SQLite, creates the tables and everything needed for test case.... I'll look some more :)