Submitted with permission from Chaofanatic, the original effect creator.

The orbit of the "Mallard" in Molten Mallard frequently desynchronizes from that of the rest of the particle.
This causes the effect to split in two, with the duck often flying away or disappearing completely.

As with most of these visual glitches, the fix is quite simple.
I have attached an updated version of item_fx.pcf with the following changes:
- The "Movement Rotate Particle Around Axis" operator of the "unusual_eotl_orbiting_burning_duck" particle has been removed
- The value of the "control_point_number" parameter of the "Movement Lock to Control Point" operator of the "unusual_eotl_orbiting_burning_duck" particle has been changed from 0 to 1
- This locks the movement of the duck to that of the rest of the effect, and solves all movement issues with the effect.