1. Jackstall occurs when the aerodynamic loads on the blades overpower the hydraulic jacks controlling the swashplate, causing control reversal. Cause and symptoms similar to RBS.
2. The roll during zero - g conditions is due to the sideways push of the tail rotor creating a rolling moment about the head (think back to tail rotor drift and roll u studied at groundschool).
3. Anything less than +ve g and helicopters definitely do not mix