When saving a file to DWG format, the cells in the file are not saved to Shared Cells, but rather remain Normal Cells.
In the General tab of the DWG Options dialog box, go to Advanced > Application Data and check to see if "Save Application Data" is toggled On.
When working in a vertical application, such as Triforma and GeoPAK, it is necessary for certain types of cells to remain Normal Cells in order to work on the cells in the resultant DWG file with the vertical application loaded.
By toggling On " Save Application Data", a linkage is written to the Shared Cell which allows it to be a Normal Cell while the DWG file is opened in MicroStation.
The linkage is ignored by AutoCAD and the cells are normal blocks when the DWG file is opened.
This is from the delivered Help:Save Application Data - If on, saves element attribute linkages to DWG XData, and saves application elements (Type 66, Level 20) to XRecords.
When the DWG file is opened in MicroStation, this non-displayable application data is automatically restored to the file.
In other words, XData is converted back to the original linkages, and application elements are created from the XRecords.