Clover used to do this when visiting at my friend's house - it was excitement at seeing her little poodle mate there to play with! I used to have to be extra vigilant and take her out more often than normal and ensure she did do a wee before I let her back in, all the while we were there. She didn't do it at home but it was very embarrassing when she peed on my friend's cream carpet and vynil flooring! I'm sure my friend thought she wasn't house trained properly! She did grow out of it though, thankfully,and doesn't ever do it now. Phew!