After upgrading from 4.0.16 to 4.0.18 My double fields now have info like "2.055313086699586e-320" where it used to be "4". It appears to be any field that had a zero length because all my datetime types are now all missing the data that was previously there. What causes this?

They may have changed some internal data structures or actual disk structures, but I tend to doubt this. Check the change log in the manual for more details.