Also, none of the versions of PopcornFX automatically inherit the velocity of the parent actor. It always has to be done explicitly.
Just to be clear you expect the particles to stay fixed in space, but as the actor moves, the particles it drops behind are also moving slightly ?
Shoot us a mail at firstname.lastname@example.org referencing this thread, attaching your effect exported as a .pkkg from the popcorn editor, we'll take a look at it, see if we can spot the issue.
Last question: you're running this in which game engine?