The parts and family system can define different levels for forward, cut, reflected and centerline graphics.
In V8i non-Dynamic View based workflows the Drawing Extraction Manager (DEM) created new elements in a separate file, this was not a problem. However, Dynamic Views do not create new elements or create separate files, as the same data is just displayed in a different presentation.
The problem is that these alternate presentations cannot be created on levels that do not already exist. Therefore the dataset is scanned for undefined levels, which are then added to the DGN-file. As a result, users may have levels in their DGN-files that they believe they have not used.
Levels added to the active file are harvested from the Part & Family definitions for Cut Symbology, Forward/Reflected Symbology and Centerline Symbology.
This scan is performed by default to support Dynamic Views.
In V8i, when only the DEM was being used to create drawings, this scan could be disabled by setting BB_DVDATASETELEMENTS = 0 (Note that a null value will not override the default setting of 1, it must be set to 0.)
As DEM is no longer available in CONNECT Edition this variable has been deprecated, CONNECT Edition will always scan the active dataset for the levels required to sucessfully create Dynamic Views.
See Drawing Views [FAQ] (scroll down or search for BB_DVDATASETELEMENTS) for more background.
Managing dgnlib files also suggests how to avoid levels being copied into dgnlibs when you are making changes to them.
See also: Dynamic View Creation Affected by Compress Options