-90 is correct, since -90 is up. The issue is when the bullet behavior has a speed of zero, then setting the angle of motion has no effect, it will always become 0 (right). The solution is to set the speed first, then the angle of motion.
The reason behind this is the bullet behavior stores velocity in two variables: vx and vy, the first being for horizontal velocity and the other for vertical. When the speed is zero then:
The angle of motion is set by first calculating the current speed with the Pythagorean theorem: speed=sqrt(vx^2+vy^2)
next the new velocity is set in the angle you want:
vx = speed*cos(angle)
vy = speed*sin(angle)
But since the speed is zero vx and vy will become zero.