As per a conversation with @mostolog in the mailing list, the following snippet in the documentation does not seem to be 100% clear:
To ensure that jobs are not dispatched by non-admin nodes you may also want to set:
dispatchinterval=0
It could be easily interpreted as "the setting may be applied to all nodes" instead of "the setting may be applied to all nodes, except the admin".
We should really make the admin node default to a non-zero dispatch interval, and everything else default to 0, so people don't have to spend so much time reading documentation (which should still be made clearer, of course).