"Anybody trying to sideslip a Jodel with flaps might be in for some nice tumbling if they don't keep the speed high. (They flick around like clockwork if you go too slow.)"
No experience with flap Jodels, but over 1500 hours on DR1050 with airbrakes. Nothing in the manual, but I'd read reports of a "flick" which is harmless. I've never managed to induce it while trying to do so, but, as pax, with the pilot sidesliping and airbrakes out, suddenly the wings flicked level. The pilot had never heard of this, and was surprised but not concerned.
The suggested cause is airflow blanking by the fuselage with the underwing airbrakes out.
It may depend on AUW and CofG. That was on the annual air test at near max AUW.