Matthew, tough question. The key to the difficulty is that it only happens sometimes. Does it happen to only certain task(s)? When you push remaining work to the future, Project updates the Resume field to indicate when remaining work is to begin again. Keep an eye on this field and see what happens. There are calculation options in the advanced tab if you want to check that these are unselected (but they are by default). Not sure what else could do this. Let me know if any of this helps.