Liz, every time my X has done this, I call him and address it. I do it nicely, just saying something along the lines of hey, can you communicate this with me instead of the kids just to make sure we are all on the same page?
He was receptive b/c I made sure to feel like I was not "blaming" him. Even though I do. I have just learned that there is a certain way to communicate with him if I want things done effectively. Sad, but true.