The particle system has its initial velocity and its velocity/life in world space. It is expected that the particle's orientation won't influence the particle's velocity. That isn't the case though as rotating the emitter clearly changes the direction of the particles. It isn't always consistent with each axis either. Meaning as you rotate the system the particle's direction don't seem to match at a 1:1 ratio.
The particles will shoot downward then begin to fly upwards.
The particles shoot upward and begin to fly downward.
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