Hai, Prominent, thank you for the response.
After a good night sleep, today I've found the reason. It happens when the bullet speed is 0.
I'm developing a simple asteroid Game and would like to have a bouncing effect when my ship hits an asteroid. I tried to apply physic behavior to my ship. But it doesn't work well together with custom movement and wrap behavior.
Yesterday I learned about the bullet bouncing off object, but now I realize it has problem in 0 speed. And it bounce without considering any mass or speed of an object, which can only be found in physic behavior.
I'm confused now how to make this works. Well I guess that will be another topic.