The odd thing is that this is happening for most of the particle effects in the game. i.e. you can see the fire doing the same things. I thought this might have something to do with running int he editor but I get this in release builds too.
I isolated the problem down to the Dynamic Decals package from the Asset Store version 2.0.2, when I upgraded to 2.0.3 this went away. As soon as a decal appeared on the screen this happened. It seems to have deeply disrupted the particle system. I may by worth investigating why two unrelated systems would malfunction like this. But for right now I am fine.