Standing on any pressure plate (except stone) while throwing a lingering potion on the ground near you causes the pressure plate to stay held down for the duration the lingering potion is in effect.
Reproducing:
Step1: Place Pressure Plate(except stone)
Step2: Stand on pressure plate
Step3: Throw lingering potion(any) on yourself.
Step4: Pressure Plate will stay held down.
This is not a bug, this is intended. The wooden pressure plates are pressed by entitites (even single a dropped item) - the lingering potion is an entity.