Hi Steve - if the objects that you were working with became open surfaces instead of a closed volume, that will make the booleans behave differently since they're mostly oriented towards working on closed volume objects.

So if you run into this again, look at the object type indicator when your objects are selected - that's in the upper right corner of the properties panel that shows the properties of the current selected objects. If that indicator says "Surface" or "Joined Srf" that means that the object is not a closed volume, it will read "Solid" if it is closed.

Anyway, that's one thing to check on if booleans start to behave differently.

- Michael