Using the SM&M++ Bushido energy launcher (or any similar modded weapon that uses a particlejet or similar to create a trail of particles behind a projectile), shoot something solid. The particlejet trail (because SM&M++ uses the older style) passes through the object for a certain period of time. This happens with stock effects as well, but it's not as noticeable.
It should be possible to eventually add collision detection to these graphical particles to make the entire projectile/exhaust combo stop where it should do.
If the engine is already supposed to do this, it may be linked to https://ministry.kronosaur.com/record.hexm?id=6047
As ICX also detects projectiles after they've died.
This effect was originally designed for missiles, which have a long vapor trail that should remain (otherwise it looks fake).
But we need a setting to turn it off.