Simples. On a regular bike your lean generates an ability for gravity to pull you down. This is offset and balanced by the centrifugal force throwing you outwards and you are able to make a turn in perfect balance with those two forces. On this machine the gravitational force is already balanced by the spring so when you add in the centrifugal force as well it throws you out of the turn.
"As far as we can tell nobody can steer the bricycle around the simple course"
pfft, as far as i can tell only a couple of academic nerds tried. I'm pretty sure i could beat your silly invisible gravity.
Very cool build though.
Can't help but think some parents are paying 10s of thousands of dollars for their 20 yr old kid to learn how to ride a bike at university.
Get rid of the pivot point.
Split their body in half balanced sitting straight. Lean to the right and don't turn the wheel, holding their body parallel to the leaning bike, HOLD the wheel straight (don't turn it) and the bike will stray right.