I experience the same problem. When my character touches some objects, while in first person view, that are attached to the ship (furniture, doors, chests, ...) the ship gets pushed arround (even under water sometimes). This is really annoying because placing and selecting objects is often way easier in first person.
This jumping /pushing arround of the ship also happened to me when removing items that are attached to the ship (e.g. crystals), while in first person.
All observed in single player on a large ship, as that's the only one i have build so far.