This bug still exists!
Parenting a ParticleEmitter (inside a cloned part) to workspace, and calling :Emit on the same frame, will not render the particles.
This is presumably because Roblox networks the “Emit” instruction out of order, and the client tries to run the Emit before the ParticleEmitter is parented/initialized.
Adding a wait(0.05) between parenting, and calling Emit, is a workarond for now.