Answered. Not a bug,by design.
R93 and R92
Sprite with Bullet behavior will have it's bullet angle of motion set to 0 if it's speed is set to 0.
Example Capx Download
add bullet behavior to sprite
Start of layout---> set sprite bullet angle of motion to 90
every one second -->set sprite bullet speed to 0
"check sprite angle of motion" it's set to zero
Win 7 64bit.