Despite documentation implying otherwise, only two out of the three
collection associations support the 'replace' (and by extension, '=')
method. The third, HasManyThroughAssociation, does not.
Fortunately, it is pretty easy to add the support. I've done that
with my patch (failing tests included) posted on this ticket:
Please take a look and consider supporting this patch.
...and we thank you for your support.