JD 2320 200cx loader hyd quick connect leaks only when not running

[Northern MN]

I don't see a leak when operating but when I put it away I get fluid on the floor from one of the connectors. I ordered some Pioneer O rings which may solve the issue.
My question- Why would a connector leak only when not under pressure?? When I park the tractor I release all the pressure from the system.

 

[ericm979]

Gravity can be applying pressure to the cylinders if the bucket is not flat on the ground.