The issue is when you try to infect a creature with Liquid Shadow that already has the Vampire ability. In your case you used it on a creature with innate Vampirism, causing the opponent to think no damage is done. In the case of using it on a creature that already has infection one side shows only one infection counter while the one using LS shows multiple:
Before
(http://imageplay.net/img/tya22264200/LSbug1.png)
After
(http://imageplay.net/img/tya22264199/LSbug2.png)
As you can see by observing both sides, an undetected desynch happens. This just happened to happen during a war match, too.