Thanks Jean, I managed to manually patch the mod_cluster-1.2.3.Final that comes with AS7.2.0; that seems to solve the problem.
This brings me now to another question that I have been keeping on the side: a systematic httpd segment fault that occurs in mod_proxy_cluster when I try to use a simple web application. Being an unrelated issue, I will open a new discussion about that.
for the core please open a JIRA.