If you opena new module and don't change any of the values on the left hand side of the design module such as type, grade, species, size, deflections, etc. when you close the module it will not ask you to save it.
This bug happens when you open a design module and only change the loads and will be fixed in both StruCalc 8.0 and 9.0 when it is released.
This problem appears to only have been affecting the Multi-Loaded Multi-Span Beam Design Module in StruCalc 8.0 releases for certain of the load input boxes. It has been addressed in StruCalc 9.0.