Thanks for the fast reply. We observed some time ago on an environment, but right now I don't have the means to reproduce it, unfortunately. I just looked into the report from the time, and it was easy to reproduce by just installing e.g. 5.6.3 from github and using the libjson-c-dev version 0.15.2. The version 0.12 worked. 5.6.3 is of course also now a bit older.