When making changes to reference levels, you may run into the following message:
Changes to attachment levels will only be valid for this session.
Should this be the case, then the keyin SET REFLEVELOVERRIDES is more than likely turned off.
For additional information refer to: Overriding and Resynchronizing Level Attributes TechNote
In addition, the following is snipped from Help:
The ability to save changes to reference file levels is controlled by either of these key-in commands:
AutoCAD: DWG VISRETAIN [0 or 1] MicroStation: SET REFLEVELOVERRIDES [OFF or ON]
If DWG VISRETAIN is set to 0 (or SET REFLEVELOVERRIDES OFF), then changes to reference file levels are retained only during the current session.
If DWG VISRETAIN is set to 1 (or SETREFLEVELOVERRIDES ON), the reference levels changes are retained when the file is closed.
Making reference level changes stick