Thanks for the update but removing collections are still necessary to avoid warning messages when saving, because a dict cannot be serialized. In fact, before 0.7 it is working, but with 0.7 introduction of proobuf, it has error.

hum, you have totally right ! My bad... But there is no way to avoid this, keep dict values in a different way ? This workaround add a slowness in the save process, no ?

Yes, it is pretty hacky, I would love to find a better workaround! The slowing down should be limited (There are not that much data into these collection), and only occur when saving a model.