Cavaliers and wet heads

I have owned two male Welsh Springer Spaniels who both had a peculiar habit that I've never had explained. On off-lead walks, whenever we encountered a Cavalier King Charles Spaniel, both dogs would pee on these little dogs heads. It was most embarrassing.
Neither dog was alive when the other was so it wasn't learned behaviour.
Never happened when we met any other breed of dog - probably happened 20 plus times over many years.
Any clues?
Graham Smith, Chobham, Surrey