I know horses, mares in particular, who seem to like to wait and pee as soon as they get in the stall. Our two do that, or they come in from pasture and pee in the lean-to. Makes us crazy.
I think mares like to pee in deep bedding so it doesn't splash on their legs :~D
Here I thought they just wanted our company cleaning stalls :) Makes sense though, I always wondered what their problem was.
Then I think this horse has an identity issue, because he's a gelding. :-)