s3_motorSet sometimes advances a wheels position, when changing speed from 0 to 0

[dlcarrier]

The s3_motorSet command, in s3.c, may advance either wheel's position, when the speed is changed from 0 to 0, while the other wheel is set to a non-zero speed. The following program repeatedly sets the left wheel speed to 25, and the right one to 0, but the right wheel advances often enough with each call to have noticeable movement:

#include "simpletools.h"
#include "s3.h"

int main() {
  s3_setup();
  while(1){
    pause(10);
    s3_motorSet(25, 0, 0);
  }    
}

Each call to s3_motorSet appears to have a change of advancing the right wheel, and while frequent calls make the movement obvious, it is still noticeable on any individual call where the uncommanded position advancement occurs.