Tangential Velocity error

I’m using 2.49.

I’ve assigned a tangential velocity to particles on a circles.

The problem is there in an entire quadrant of particles missing. That is, when the simulation happens there is a 90 area where particles do not go. So instead of a circle as you’d expect, there is a pie with a 4th missing.

Are there any possible reasons for this? Is there something I’m missing?