From Valve Developer Community
Q: I have an instantaneously emitted particle with a long lifetime that's supposed to attach to an object, but it's getting left behind when the object moves.
- A: Add a position_lock_to_controlpoint operator with a control point of 0. By default that control point is the emitter.
Q: When I used the rope render type, it flickers around for some reason!
- A: Rope rendering clicks onto the nearest particle when a particle dies, the only solution is to destroy and create all particles simultaneously. Another solution seems to be adding a Velocity Noise initializer - it's tricky to work with, but it seems to work. Note: this problem does not exist in the L4D2 or Alien Swarm engine branches.