Now, that was dumb. A 185 has bladders, and leaving the caps off can
pull the bladder retention snaps off inside the wing and collapse the
tank. Filling a partially collapsed tank can mislead the pilot into
thinking he has full tanks, and water can get trapped in the resulting
wrinkles along the bottom. If the bottom is pulled up some, it will
hold the fuel level sender up and give erroneous gauge indications.
Those bladders need inspection after such an event.
Most bladder-equipped Cessnas have an AD against the fuel caps
forcing an annual inspection of the o-ring seal. A broken or crumbling
seal can do the same thing as a missing cap: draw air out of the tank
faster than the vent can balance the pressure, and
fuel loss is the result.

Dan