I have had a JP5 (no tip tanks) in an inadvertent inverted spin after attempting to enter an erect spin on an up vertical line for a spin from a manoeuvre.
Perhaps it's no coincidence that my inverted spin was induced via a very badly botched stall turn - in retrospect (from what I could remember happening) I managed to induce a flick manoeuvre on the way up by not getting the true vertical early enough and then trying to correct it using a lot of up elevator. As soon as I put on rudder, the aircraft auto-rotated. It fell out on its back and then spun inverted. I do remember recognising that it was inverted quite promptly (I had seen it before in the C150, as previously mentioned) and putting in some aft stick and full opposite rudder, when it came out after a few turns (no idea how many). We students had received no guidance on how to recover from an inverted spin.
I then found myself in an erect spin because I was slow getting the rudder and aft stick off and I think it reversed direction, too. I lost a lot of height. I flew straight and level for quite a while afterwards while I recovered my composure then went back to base!