Argh! I write this in hopes that I save somebody a few ounces of milk.
The seams of frozen milk bags sometimes split and you don't know that they've split until the milk has thawed and has spilled all over the place or if you thaw within a container of warm water like I do, water has mixed in with the milk left in the bag.
When thawing milk, put it inside a second ziplock bag so if the frozen milk bag has a hole in it, any leaking milk will leak into the second bag and not be contaminated by anything.
You're welcome. Damnit.