Motion blur does not work while spawning

[mitchfx]

Are new particles spawning until frame 17? Moblur isn't supported for topology-changing geo (yet) so you're not seeing it until the vert/face count stops changing.

Is there a way around this? King of need to have blur while it is spawning?

Try setting your motion blur interval center to 0.5 instead of 0.0 to get around this.  That sometimes works for me when the particle count is changing.