I quite see that people would think it's the (burning rubber) tire but the foot is very gentle especially since it happened the first time. A momentary break in traction on a hill start wouldn't burn rubber anyway.
I did let the hand brake catch for a second but couldn't be sure if it was that, as I don't yet know how it works on this 3 wheeler set up.
The second and third time, there was no use of handbrake.
Treating with kid gloves as I do my old bikes.
