Problems of using L298n with Scratch

[Cosworth431]

I am using L298n (the red one with 8 input pins) to control a 4tronix robot. I managed to get the thing moving forward by Scratch and both motors turn. However when I tried to get to go the other way, one side of the motor does not turn and the other side of motor can turn to opposite direction as expected. I used python the test the motors and both motors can turn the both directions, so the motors themselves are fine.
PS The motor with problems turn uncontrollably when I started Scratch and does not stop until I used another python problem to kill it. Maybe that has something to do with it, can anyone help? Thanks a lot

[timrowledge]

You might get some scratch related help if you cross-post this to the Scratch forum.