2002 Honda Civic coolant coming out of coolant reservoir after shut engine off

The car does not overheat and is fine when it is on. Once the car is shut off, sometimes (50/50) coolant will escape from the reservoir cap, it is hot, it looks clean. What could this be? We just changed the rad cap and that didnt fix it. About enough coolant to fill a shot glass or 2 spills out.