My Kohler Command 12.5 in a 1993 John Deere STX38 riding mower does this same thing intermittently.
I believe it was the anti-drain back of the oil filter letting oil rise in the sump while sitting (similar to being overfilled) and leaking past the rings or valve stem seals.
or maybe the random spot in the cylinder that the piston sits, may be worn and letting oil pass by the rings while sitting.
An oil change with a new filter seemed to resolve this for me.