Hey Scmb,
I have to tell you as a single dad of over ten years... kids remember, learn, and grow from their experiences. If this is how your ex is it will come back and bite her in the backside at some point from the kids themselves....
I certainly understand the anger your feeling, the best thing I found to deal with the intermitten absense of my kids is to take full advantage of the time they are with me... make your next full day with them "fathers day"....
good luck to you......
dave...........