# funny behaviour or what - dc motor control

I'm trying to control the speed of this motor, with this motor driver and pic16f690.

pwm in my program

5 kHz frequency (0.2 ms period)


Starting with 50% duty cycle the motor doesn't run. But moving from say, 80% to 50% (i.e. program my PIC with 80% duty cycle, and then re-program it with 50%), the motor will run at 50% (of course at a lower speed). I consider this funny. Anyone to explain this?